Merge branch 'jungin' into 'main'

assignment 6-7-8-10 See merge request kaist-cp-class/cs220-private!14
2025-12-12 21:08:45 +00:00 · 2023-08-20 13:10:04 +00:00
parent 3ef3cae0cd ee1f7d0b8f
commit a3da118cf5
40 changed files with 2624 additions and 310 deletions
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -227,6 +227,7 @@ dependencies = [
 "num-traits",
 "pest",
 "pest_derive",
+ "rand",
 "rayon",
 "thiserror",
 ]
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -20,3 +20,4 @@ approx = "0.5.1"
 num-traits = "0.2"
 ndarray = "0.15.0"
 ndarray-rand = "0.14.0"
+rand = "0.8.5"
--- a/scripts/grade-06.sh
+++ b/scripts/grade-06.sh
@@ -9,12 +9,12 @@ BASEDIR=$(dirname "$0")
 source $BASEDIR/grade-utils.sh

 RUNNERS=(
-    "cargo"
-    "cargo --release"
-    "cargo_asan"
-    "cargo_asan --release"
-    "cargo_tsan"
-    "cargo_tsan --release"
+	"cargo"
+	"cargo --release"
+	"cargo_asan"
+	"cargo_asan --release"
+	"cargo_tsan"
+	"cargo_tsan --release"
 )

 # Lints.
@@ -22,12 +22,12 @@ run_linters || exit 1

 # Executes test for each runner.
 for RUNNER in "${RUNNERS[@]}"; do
-    echo "Running with $RUNNER..."
+	echo "Running with $RUNNER..."

-    TESTS=("--lib assignment06_grade")
-    if [ $(run_tests) -ne 0 ]; then
-        exit 1
-    fi
+	TESTS=("--lib assignment06")
+	if [ $(run_tests) -ne 0 ]; then
+		exit 1
+	fi
 done

 exit 0
--- a/scripts/grade-07.sh
+++ b/scripts/grade-07.sh
@@ -9,12 +9,12 @@ BASEDIR=$(dirname "$0")
 source $BASEDIR/grade-utils.sh

 RUNNERS=(
-    "cargo"
-    "cargo --release"
-    "cargo_asan"
-    "cargo_asan --release"
-    "cargo_tsan"
-    "cargo_tsan --release"
+	"cargo"
+	"cargo --release"
+	"cargo_asan"
+	"cargo_asan --release"
+	"cargo_tsan"
+	"cargo_tsan --release"
 )

 # Lints.
@@ -22,12 +22,12 @@ run_linters || exit 1

 # Executes test for each runner.
 for RUNNER in "${RUNNERS[@]}"; do
-    echo "Running with $RUNNER..."
+	echo "Running with $RUNNER..."

-    TESTS=("--lib assignment07_grade")
-    if [ $(run_tests) -ne 0 ]; then
-        exit 1
-    fi
+	TESTS=("--lib assignment07")
+	if [ $(run_tests) -ne 0 ]; then
+		exit 1
+	fi
 done

 exit 0
--- a/scripts/grade-09.sh
+++ b/scripts/grade-09.sh
@@ -9,12 +9,12 @@ BASEDIR=$(dirname "$0")
 source $BASEDIR/grade-utils.sh

 RUNNERS=(
-    "cargo"
-    "cargo --release"
-    "cargo_asan"
-    "cargo_asan --release"
-    "cargo_tsan"
-    "cargo_tsan --release"
+	"cargo"
+	"cargo --release"
+	"cargo_asan"
+	"cargo_asan --release"
+	"cargo_tsan"
+	"cargo_tsan --release"
 )

 # Lints.
@@ -22,12 +22,12 @@ run_linters || exit 1

 # Executes test for each runner.
 for RUNNER in "${RUNNERS[@]}"; do
-    echo "Running with $RUNNER..."
+	echo "Running with $RUNNER..."

-    TESTS=("--lib assignment09_grade")
-    if [ $(run_tests) -ne 0 ]; then
-        exit 1
-    fi
+	TESTS=("--lib assignment09")
+	if [ $(run_tests) -ne 0 ]; then
+		exit 1
+	fi
 done

 exit 0
--- a/scripts/grade-10.sh
+++ b/scripts/grade-10.sh
@@ -9,12 +9,12 @@ BASEDIR=$(dirname "$0")
 source $BASEDIR/grade-utils.sh

 RUNNERS=(
-    "cargo"
-    "cargo --release"
-    "cargo_asan"
-    "cargo_asan --release"
-    "cargo_tsan"
-    "cargo_tsan --release"
+	"cargo"
+	"cargo --release"
+	"cargo_asan"
+	"cargo_asan --release"
+	"cargo_tsan"
+	"cargo_tsan --release"
 )

 # Lints.
@@ -22,12 +22,12 @@ run_linters || exit 1

 # Executes test for each runner.
 for RUNNER in "${RUNNERS[@]}"; do
-    echo "Running with $RUNNER..."
+	echo "Running with $RUNNER..."

-    TESTS=("--lib assignment10_grade")
-    if [ $(run_tests) -ne 0 ]; then
-        exit 1
-    fi
+	TESTS=("--lib assignment10")
+	if [ $(run_tests) -ne 0 ]; then
+		exit 1
+	fi
 done

 exit 0
--- a/scripts/grade-11.sh
+++ b/scripts/grade-11.sh
@@ -24,7 +24,7 @@ run_linters || exit 1
 for RUNNER in "${RUNNERS[@]}"; do
    echo "Running with $RUNNER..."

-    TESTS=("--lib assignment11")
+    TESTS=("--lib assignment11_grade")
    if [ $(run_tests) -ne 0 ]; then
        exit 1
    fi
--- a/scripts/grade-12.sh
+++ b/scripts/grade-12.sh
@@ -24,7 +24,7 @@ run_linters || exit 1
 for RUNNER in "${RUNNERS[@]}"; do
    echo "Running with $RUNNER..."

-    TESTS=("--lib assignment11")
+    TESTS=("--lib assignment12_grade")
    if [ $(run_tests) -ne 0 ]; then
        exit 1
    fi
--- a/src/assignments/assignment06/mod.rs
+++ b/src/assignments/assignment06/mod.rs
@@ -0,0 +1,16 @@
+//! Assignment 6: Mastering advanced types (1/2).
+//!
+//! The primary goal of this assignment is to understand generics, traits, and lifetimes.
+//!
+//! You should fill out the `todo!()` placeholders in such a way that `/scripts/grade-06.sh` works fine.
+//! See `assignment06_grade.rs` and `/scripts/grade-06.sh` for the test script.
+
+use std::{collections::HashMap, fmt::Debug};
+
+pub mod semiring;
+pub mod square_matrix;
+pub mod symbolic_differentiation;
+
+mod semiring_grade;
+mod square_matrix_grade;
+mod symbolic_differentiation_grade;
--- a/src/assignments/assignment06/semiring.rs
+++ b/src/assignments/assignment06/semiring.rs
@@ -1,9 +1,4 @@
-//! Assignment 6: Mastering advanced types (1/2).
-//!
-//! The primary goal of this assignment is to understand generics, traits, and lifetimes.
-//!
-//! You should fill out the `todo!()` placeholders in such a way that `/scripts/grade-06.sh` works fine.
-//! See `assignment06_grade.rs` and `/scripts/grade-06.sh` for the test script.
+//! Semiring

 use std::{collections::HashMap, fmt::Debug};

@@ -123,12 +118,6 @@ impl<C: Semiring> Semiring for Polynomial<C> {
    }
 }

-impl<C: Semiring> From<C> for Polynomial<C> {
-    fn from(value: C) -> Self {
-        todo!()
-    }
-}
-
 impl<C: Semiring> Polynomial<C> {
    /// Constructs polynomial `x`.
    pub fn x() -> Self {
@@ -139,4 +128,41 @@ impl<C: Semiring> Polynomial<C> {
    pub fn eval(&self, value: C) -> C {
        todo!()
    }
+
+    /// Constructs polynomial `ax^n`.
+    pub fn term(a: C, n: u64) -> Self {
+        todo!()
+    }
+}
+
+impl<C: Semiring> From<C> for Polynomial<C> {
+    fn from(value: C) -> Self {
+        todo!()
+    }
+}
+
+/// Given a string `s`, parse it into a `Polynomial<C>`.
+/// You may assume that `s` follows the criteria below.
+/// Therefore, you do not have to return `Err`.
+///
+/// Assumptions:
+/// - Each term is separated by ` + `.
+/// - Each term is one of the following form:
+///   `a`, `x`, `ax`, `x^n`, and `ax^n`,
+///   where `a` is a `usize` number and `n` is a `u64` number.
+///   This `a` should then be converted to a `C` type.
+/// - In `a`, it is guaranteed that `a >= 1`.
+/// - In `ax` and `ax^n`, it is guaranteed that `a >= 2`.
+/// - In `x^n` and `ax^n`, it is guaranteed that `n >= 2`.
+/// - All terms have unique degrees.
+///
+/// Consult `assignment06_jaemin_choi_grade.rs` for example valid strings.
+///
+/// Hint: `.split`, `.parse`, and `Polynomial::term`
+impl<C: Semiring> std::str::FromStr for Polynomial<C> {
+    type Err = (); // Ignore this for now...
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        todo!()
+    }
 }
--- a/src/assignments/assignment06/semiring_grade.rs
+++ b/src/assignments/assignment06/semiring_grade.rs
@@ -1,6 +1,14 @@
 #[cfg(test)]
 mod test {
-    use super::super::assignment06::*;
+    use super::super::semiring::*;
+    use ntest::assert_about_eq;
+
+    fn test_from_str(s: &str, f: impl Fn(i64) -> i64) {
+        let poly = s.parse::<Polynomial<i64>>().unwrap();
+        for i in 0..10 {
+            assert_eq!(poly.eval(i), f(i));
+        }
+    }

    fn test_polynomial<T: Semiring>() {
        // x^2 + 5x + 6
@@ -21,6 +29,43 @@ mod test {
        assert_eq!(value, from_usize(13 * 13 + 5 * 13 + 6));
    }

+    #[test]
+    fn test_123() {
+        test_from_str("123", |x| 123);
+    }
+
+    #[test]
+    fn test_x() {
+        test_from_str("x", |x| x);
+    }
+
+    #[test]
+    fn test_24x() {
+        test_from_str("24x", |x| 24 * x);
+    }
+
+    #[test]
+    fn test_2x_3() {
+        test_from_str("2x + 3", |x| 2 * x + 3);
+    }
+
+    #[test]
+    fn test_x3() {
+        test_from_str("x^3", |x| x * x * x);
+    }
+
+    #[test]
+    fn test_2x3_3x2_5x_12() {
+        test_from_str("2x^3 + 3x^2 + 5x + 12", |x| {
+            2 * x * x * x + 3 * x * x + 5 * x + 12
+        });
+    }
+
+    #[test]
+    fn test_x5_1() {
+        test_from_str("x^5 + 1", |x| x * x * x * x * x + 1);
+    }
+
    #[test]
    fn test_polynomial_u64() {
        test_polynomial::<u64>();
--- a/src/assignments/assignment06/square_matrix.rs
+++ b/src/assignments/assignment06/square_matrix.rs
@@ -0,0 +1,88 @@
+//! Square matrix
+
+/// Square matrix
+pub trait SquareMatrix {
+    /// The type of the submatrix of this square matrix.
+    /// For example, the submatrix of a 3 x 3 matrix is a 2 x 2 matrix.
+    /// https://en.wikipedia.org/wiki/Matrix_(mathematics)#Submatrix
+    type Submatrix;
+
+    /// Returns the submatrix obtained by removing the `row`th row and `col`th column
+    /// from the original matrix.
+    /// https://en.wikipedia.org/wiki/Matrix_(mathematics)#Submatrix
+    fn sub_matrix(&self, row: usize, col: usize) -> Self::Submatrix;
+
+    /// Returns the determinant of the matrix.
+    fn det(&self) -> i64;
+
+    /// Returns the determinant of ab, where a is self, b is given, and ab is the matrix product of them.
+    /// Note that the size of a and b are the same.
+    /// Hint: Use the fact that det(ab) = det(a) * det(b)
+    /// https://en.wikipedia.org/wiki/Determinant#Multiplicativity_and_matrix_groups
+    fn det_ab(&self, b: &Self) -> i64 {
+        todo!()
+    }
+}
+
+/// 2 x 2 matrix
+#[derive(Debug, PartialEq)]
+pub struct Mat2 {
+    /// inner is a 2 dimensional array (size: 2 x 2)
+    pub inner: [[i64; 2]; 2],
+}
+
+impl SquareMatrix for Mat2 {
+    type Submatrix = i64;
+
+    fn sub_matrix(&self, row: usize, col: usize) -> Self::Submatrix {
+        // Hint: The submatrix of a 2 x 2 matrix is simply a single number.
+        todo!()
+    }
+
+    // Hint: https://en.wikipedia.org/wiki/Determinant
+    fn det(&self) -> i64 {
+        todo!()
+    }
+}
+
+/// 3 x 3 matrix
+#[derive(Debug, PartialEq)]
+pub struct Mat3 {
+    /// inner is a 2 dimensional array (size: 3 x 3)
+    pub inner: [[i64; 3]; 3],
+}
+
+impl SquareMatrix for Mat3 {
+    type Submatrix = Mat2;
+
+    fn sub_matrix(&self, row: usize, col: usize) -> Self::Submatrix {
+        todo!()
+    }
+
+    // Hint: Use the determinant of the sub-matrices.
+    // https://semath.info/src/determinant-three-by-three.html
+    fn det(&self) -> i64 {
+        todo!()
+    }
+}
+
+/// 4 x 4 matrix
+#[derive(Debug, PartialEq)]
+pub struct Mat4 {
+    /// inner is a 2 dimensional array (size: 4 x 4)
+    pub inner: [[i64; 4]; 4],
+}
+
+impl SquareMatrix for Mat4 {
+    type Submatrix = Mat3;
+
+    fn sub_matrix(&self, row: usize, col: usize) -> Self::Submatrix {
+        todo!()
+    }
+
+    // Hint: Use the determinant of the sub-matrices.
+    // https://semath.info/src/determinant-four-by-four.html
+    fn det(&self) -> i64 {
+        todo!()
+    }
+}
--- a/src/assignments/assignment06/square_matrix_grade.rs
+++ b/src/assignments/assignment06/square_matrix_grade.rs
@@ -0,0 +1,72 @@
+#[cfg(test)]
+mod test {
+    use super::super::square_matrix::*;
+    use ntest::assert_about_eq;
+
+    #[test]
+    fn test_mat2() {
+        let mat = Mat2 {
+            inner: [[1, 2], [3, 4]],
+        };
+        assert_eq!(mat.sub_matrix(1, 1), 4);
+        assert_eq!(mat.sub_matrix(1, 2), 3);
+        assert_eq!(mat.sub_matrix(2, 1), 2);
+        assert_eq!(mat.sub_matrix(2, 2), 1);
+        assert_eq!(mat.det(), -2);
+
+        let mat2 = Mat2 {
+            inner: [[2, 3], [5, 7]],
+        };
+        assert_eq!(mat.det_ab(&mat2), mat.det() * mat2.det());
+    }
+
+    #[test]
+    fn test_mat3() {
+        let mat = Mat3 {
+            inner: [[1, 2, 3], [5, 5, 6], [7, 8, 10]],
+        };
+        assert_eq!(
+            mat.sub_matrix(1, 2),
+            Mat2 {
+                inner: [[5, 6], [7, 10]]
+            }
+        );
+        assert_eq!(mat.det(), 1);
+
+        let mat2 = Mat3 {
+            inner: [[2, 3, 5], [7, 10, 11], [12, 14, 20]],
+        };
+        assert_eq!(mat2.det(), -42);
+        assert_eq!(mat.det_ab(&mat2), mat.det() * mat2.det());
+    }
+
+    #[test]
+    fn test_mat4() {
+        let mat = Mat4 {
+            inner: [
+                [1, 11, 3, 4],
+                [5, 6, 7, 9],
+                [25, 10, 11, 20],
+                [36, 14, 15, 30],
+            ],
+        };
+        assert_eq!(
+            mat.sub_matrix(2, 3),
+            Mat3 {
+                inner: [[1, 11, 4], [25, 10, 20], [36, 14, 30]]
+            }
+        );
+        assert_eq!(mat.det(), 2089);
+
+        let mat2 = Mat4 {
+            inner: [
+                [2, 3, 5, 5],
+                [7, 10, 11, 20],
+                [12, 14, 20, 30],
+                [1, 2, 5, 10],
+            ],
+        };
+        assert_eq!(mat2.det(), -340);
+        assert_eq!(mat.det_ab(&mat2), mat.det() * mat2.det());
+    }
+}
--- a/src/assignments/assignment06/symbolic_differentiation.rs
+++ b/src/assignments/assignment06/symbolic_differentiation.rs
@@ -0,0 +1,360 @@
+//! Symbolic differentiation with rational coefficents.
+
+use std::fmt;
+use std::ops::*;
+
+/// Rational number represented by two isize, numerator and denominator.
+///
+/// Each Rational number should be normalized so that `demoninator` is nonnegative and `numerator` and `demoninator` are coprime.
+/// See [`normalize`] for examples. As a corner case, 0 is represented by Rational { numerator: 0, demoninator: 0 }.
+///
+/// For "natural use", Rational also overloads standard arithmetic operations, i.e, `+`, `-`, `*`, `/`.
+///
+/// See [here](https://doc.rust-lang.org/core/ops/index.html) for details.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct Rational {
+    numerator: isize,
+    denominator: isize,
+}
+
+// Some useful constants.
+
+/// Zero
+pub const ZERO: Rational = Rational::new(0, 0);
+/// One
+pub const ONE: Rational = Rational::new(1, 1);
+/// Minus one
+pub const MINUS_ONE: Rational = Rational::new(-1, 1);
+
+impl Rational {
+    /// Creates a new rational number.
+    pub const fn new(numerator: isize, denominator: isize) -> Self {
+        Self {
+            numerator,
+            denominator,
+        }
+    }
+}
+
+impl Add for Rational {
+    type Output = Self;
+
+    fn add(self, rhs: Self) -> Self::Output {
+        todo!()
+    }
+}
+
+impl Mul for Rational {
+    type Output = Self;
+
+    fn mul(self, rhs: Self) -> Self::Output {
+        todo!()
+    }
+}
+
+impl Sub for Rational {
+    type Output = Self;
+
+    fn sub(self, rhs: Self) -> Self::Output {
+        todo!()
+    }
+}
+
+impl Div for Rational {
+    type Output = Self;
+
+    fn div(self, rhs: Self) -> Self::Output {
+        todo!()
+    }
+}
+
+/// Differentiable functions.
+///
+/// For simplicity, we only consider infinitely differentiable functions.
+pub trait Differentiable: Clone {
+    /// Differentiate.
+    ///
+    /// Since the return type is `Self`, this trait can only be implemented
+    /// for types that are closed under differentiation.
+    fn diff(&self) -> Self;
+}
+
+impl Differentiable for Rational {
+    fn diff(&self) -> Self {
+        todo!()
+    }
+}
+
+/// Singleton polynomial.
+///
+/// Unlike regular polynomials, this type only represents a single term.
+/// The `Const` variant is included to make `Polynomial` closed under differentiation.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum SingletonPolynomial {
+    /// Constant polynomial.
+    Const(Rational),
+    /// Non-const polynomial.
+    Polynomial {
+        /// coefficent of polynomial. Must be non-zero.
+        coeff: Rational,
+        /// power of polynomial. Must be non-zero.
+        power: Rational,
+    },
+}
+
+impl SingletonPolynomial {
+    /// Creates a new const polynomial.
+    pub fn new_c(r: Rational) -> Self {
+        todo!()
+    }
+
+    /// Creates a new polynomial.
+    pub fn new_poly(coeff: Rational, power: Rational) -> Self {
+        todo!()
+    }
+}
+
+impl Differentiable for SingletonPolynomial {
+    fn diff(&self) -> Self {
+        todo!()
+    }
+}
+
+/// Expoential function.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct Exp;
+
+impl Exp {
+    /// Creates a new exponential function.
+    pub fn new() -> Self {
+        todo!()
+    }
+}
+
+impl Default for Exp {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl Differentiable for Exp {
+    fn diff(&self) -> Self {
+        todo!()
+    }
+}
+
+/// Trigonometric functions.
+///
+/// The trig fucntions carry their coefficents to be closed under differntiation.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Trignometric {
+    /// Sine function.
+    Sine {
+        /// Coefficent
+        coeff: Rational,
+    },
+    /// Sine function.
+    Cosine {
+        /// Coefficent
+        coeff: Rational,
+    },
+}
+
+impl Trignometric {
+    /// Creates a new sine function.
+    pub fn new_sine(coeff: Rational) -> Self {
+        todo!()
+    }
+
+    /// Creates a new cosine function.
+    pub fn new_cosine(coeff: Rational) -> Self {
+        todo!()
+    }
+}
+
+impl Differentiable for Trignometric {
+    fn diff(&self) -> Self {
+        todo!()
+    }
+}
+
+/// Basic functions
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum BaseFuncs {
+    /// Constant
+    Const(Rational),
+    /// Polynomial
+    Poly(SingletonPolynomial),
+    /// Exponential
+    Exp(Exp),
+    /// Trignometirc
+    Trig(Trignometric),
+}
+
+impl Differentiable for BaseFuncs {
+    fn diff(&self) -> Self {
+        todo!()
+    }
+}
+
+/// Complex functions.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum ComplexFuncs<F> {
+    /// Basic functions
+    Func(F),
+    /// Addition
+    Add(Box<ComplexFuncs<F>>, Box<ComplexFuncs<F>>),
+    /// Subtraction
+    Sub(Box<ComplexFuncs<F>>, Box<ComplexFuncs<F>>),
+    /// Multipliciation
+    Mul(Box<ComplexFuncs<F>>, Box<ComplexFuncs<F>>),
+    /// Division
+    Div(Box<ComplexFuncs<F>>, Box<ComplexFuncs<F>>),
+    /// Composition
+    Comp(Box<ComplexFuncs<F>>, Box<ComplexFuncs<F>>),
+}
+
+impl<F: Differentiable> Differentiable for Box<F> {
+    fn diff(&self) -> Self {
+        todo!()
+    }
+}
+
+impl<F: Differentiable> Differentiable for ComplexFuncs<F> {
+    fn diff(&self) -> Self {
+        todo!()
+    }
+}
+
+/// Evaluate functions.
+pub trait Evaluate {
+    ///  Evaluate `self` at `x`.
+    fn evaluate(&self, x: f64) -> f64;
+}
+
+impl Evaluate for Rational {
+    fn evaluate(&self, x: f64) -> f64 {
+        todo!()
+    }
+}
+
+impl Evaluate for SingletonPolynomial {
+    fn evaluate(&self, x: f64) -> f64 {
+        todo!()
+    }
+}
+
+impl Evaluate for Exp {
+    fn evaluate(&self, x: f64) -> f64 {
+        todo!()
+    }
+}
+
+impl Evaluate for Trignometric {
+    fn evaluate(&self, x: f64) -> f64 {
+        todo!()
+    }
+}
+
+impl Evaluate for BaseFuncs {
+    fn evaluate(&self, x: f64) -> f64 {
+        todo!()
+    }
+}
+
+impl<F: Evaluate> Evaluate for ComplexFuncs<F> {
+    fn evaluate(&self, x: f64) -> f64 {
+        todo!()
+    }
+}
+
+impl fmt::Display for Rational {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if *self == ZERO {
+            return write!(f, "0");
+        } else if self.denominator == 1 {
+            return write!(f, "{}", self.numerator);
+        }
+        write!(f, "{}/{}", self.numerator, self.denominator)
+    }
+}
+
+impl fmt::Display for SingletonPolynomial {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::Const(r) => write!(f, "{r}"),
+            Self::Polynomial { coeff, power } => {
+                // coeff or power is zero
+                if *coeff == ZERO {
+                    return write!(f, "0");
+                } else if *power == ZERO {
+                    return write!(f, "{coeff}");
+                }
+
+                // Standard form of px^q
+                let coeff = if *coeff == ONE {
+                    "".to_string()
+                } else if *coeff == MINUS_ONE {
+                    "-".to_string()
+                } else {
+                    format!("({coeff})")
+                };
+                let var = if *power == ONE {
+                    "x".to_string()
+                } else {
+                    format!("x^({power})")
+                };
+                write!(f, "{coeff}{var}")
+            }
+        }
+    }
+}
+
+impl fmt::Display for Exp {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "exp(x)")
+    }
+}
+
+impl fmt::Display for Trignometric {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let (func, coeff) = match self {
+            Trignometric::Sine { coeff } => ("sin(x)", coeff),
+            Trignometric::Cosine { coeff } => ("cos(x)", coeff),
+        };
+
+        if *coeff == ZERO {
+            write!(f, "0")
+        } else if *coeff == ONE {
+            write!(f, "{func}")
+        } else if *coeff == MINUS_ONE {
+            write!(f, "-{func}")
+        } else {
+            write!(f, "({coeff}){func}")
+        }
+    }
+}
+
+impl fmt::Display for BaseFuncs {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::Const(r) => write!(f, "{r}"),
+            Self::Poly(p) => write!(f, "{p}"),
+            Self::Exp(e) => write!(f, "{e}"),
+            Self::Trig(t) => write!(f, "{t}"),
+        }
+    }
+}
+
+impl<F: Differentiable + fmt::Display> fmt::Display for ComplexFuncs<F> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            ComplexFuncs::Func(func) => write!(f, "{func}"),
+            ComplexFuncs::Add(l, r) => write!(f, "({l} + {r})"),
+            ComplexFuncs::Sub(l, r) => write!(f, "({l} - {r})"),
+            ComplexFuncs::Mul(l, r) => write!(f, "({l} * {r})"),
+            ComplexFuncs::Div(l, r) => write!(f, "({l} / {r})"),
+            ComplexFuncs::Comp(l, r) => write!(f, "({l} ∘ {r})"),
+        }
+    }
+}
--- a/src/assignments/assignment06/symbolic_differentiation_grade.rs
+++ b/src/assignments/assignment06/symbolic_differentiation_grade.rs
@@ -0,0 +1,216 @@
+#[cfg(test)]
+mod test {
+    use super::super::symbolic_differentiation::*;
+    use ntest::assert_about_eq;
+
+    // Constant rationals to use
+    const TWO: Rational = Rational::new(2, 1);
+    const FOUR: Rational = Rational::new(4, 1);
+    const THIRD: Rational = Rational::new(1, 3);
+    const FIVE_THIRD: Rational = Rational::new(5, 3);
+    const TWO_SEVENTH: Rational = Rational::new(2, 7);
+
+    #[test]
+    fn test_rational_simpl() {
+        assert_eq!(format!("{}", Rational::new(1, 2)), "1/2".to_string());
+
+        assert_eq!(format!("{}", Rational::new(0, 0)), "0".to_string());
+
+        assert_eq!(format!("{}", Rational::new(1, 1)), "1".to_string());
+
+        assert_eq!(format!("{}", Rational::new(-3, 7)), "-3/7".to_string());
+    }
+
+    #[test]
+    fn test_rational_arithmetic() {
+        assert_eq!(
+            format!("{}", Rational::new(1, 4) + Rational::new(3, 4)),
+            "1".to_string()
+        );
+
+        assert_eq!(
+            format!("{}", Rational::new(1, 3) + Rational::new(1, 6)),
+            "1/2".to_string()
+        );
+
+        assert_eq!(
+            format!("{}", Rational::new(1, 5) - Rational::new(1, 2)),
+            "-3/10".to_string()
+        );
+
+        assert_eq!(
+            format!("{}", Rational::new(-5, 12) * Rational::new(6, 125)),
+            "-1/50".to_string()
+        );
+
+        assert_eq!(
+            format!("{}", Rational::new(-3, 4) / Rational::new(-7, 13)),
+            "39/28".to_string()
+        );
+    }
+
+    #[test]
+    fn test_rational_arithmetic_long() {
+        assert_eq!(
+            format!(
+                "{}",
+                Rational::new(1, 2) + Rational::new(1, 2) + Rational::new(1, 2)
+            ),
+            "3/2".to_string()
+        );
+
+        assert_eq!(
+            format!(
+                "{}",
+                Rational::new(1, 2) - Rational::new(1, 4) + Rational::new(1, 5)
+            ),
+            "9/20".to_string()
+        );
+
+        assert_eq!(
+            format!(
+                "{}",
+                Rational::new(1, 2)
+                    * Rational::new(1, 4)
+                    * Rational::new(1, 8)
+                    * Rational::new(1, 16)
+                    / Rational::new(1, 1024)
+            ),
+            "1".to_string()
+        );
+
+        assert_eq!(
+            format!(
+                "{}",
+                Rational::new(123, 798)
+                    + Rational::new(684, 32) / (Rational::new(13, 44) - Rational::new(123, 4472))
+                        * Rational::new(1237, 2)
+            ),
+            "12356494070/250439".to_string()
+        );
+    }
+
+    #[test]
+    fn test_differentiate_simple() {
+        // Constant
+        assert_eq!(format!("{}", Rational::new(3, 2).diff()), "0".to_string());
+
+        // Polynomials
+        assert_eq!(
+            format!("{}", SingletonPolynomial::new_c(Rational::new(3, 1)).diff()),
+            "0".to_string()
+        );
+        assert_eq!(
+            format!("{}", SingletonPolynomial::new_poly(TWO, FOUR).diff()),
+            "(8)x^(3)".to_string()
+        );
+        assert_eq!(
+            format!(
+                "{}",
+                SingletonPolynomial::new_poly(FIVE_THIRD, THIRD).diff()
+            ),
+            "(5/9)x^(-2/3)".to_string()
+        );
+
+        // Exponential
+        assert_eq!(format!("{}", Exp::new().diff()), "exp(x)".to_string());
+
+        // Trigonometric
+        assert_eq!(
+            format!("{}", Trignometric::new_sine(ONE).diff()),
+            "cos(x)".to_string()
+        );
+        assert_eq!(
+            format!("{}", Trignometric::new_cosine(ONE).diff()),
+            "-sin(x)".to_string()
+        );
+        assert_eq!(
+            format!("{}", Trignometric::new_sine(FIVE_THIRD).diff()),
+            "(5/3)cos(x)".to_string()
+        );
+        assert_eq!(
+            format!("{}", Trignometric::new_cosine(TWO_SEVENTH).diff()),
+            "(-2/7)sin(x)".to_string()
+        );
+    }
+
+    #[test]
+    fn test_differentiate_complex() {
+        type BF = BaseFuncs;
+        type CF = ComplexFuncs<BF>;
+
+        // Unlike the above simple test, it is hard to state a canonical
+        // form for derivative of more complex functions. Thus, we only test that the
+        // derivative is correct at certain points.
+
+        // Add
+        //
+        // d/dx (2x^4 + exp(x)) = 8x^3 + exp(x)
+        let f1 = SingletonPolynomial::new_poly(TWO, FOUR);
+        let f2 = Exp::new();
+        let deriv = CF::Add(
+            Box::new(CF::Func(BF::Poly(f1))),
+            Box::new(CF::Func(BF::Exp(f2))),
+        )
+        .diff();
+        assert_about_eq!(deriv.evaluate(2.2), 94.2090134994f64);
+        assert_about_eq!(deriv.evaluate(4.5), 819.017131301);
+
+        // Sub
+        //
+        // d/dx ((5/3)cos(x) - sin(x)) = (-5/3)sin(x) - cos(x)
+        let f1 = Trignometric::new_cosine(FIVE_THIRD);
+        let f2 = Trignometric::new_sine(ONE);
+        let deriv = CF::Sub(
+            Box::new(CF::Func(BF::Trig(f1))),
+            Box::new(CF::Func(BF::Trig(f2))),
+        )
+        .diff();
+        assert_about_eq!(deriv.evaluate(2.7), 0.191772341627);
+        assert_about_eq!(deriv.evaluate(0.01), -1.01661638931);
+
+        // Mult
+        //
+        // d/dx (2x^4 * cos(x) * exp(x)) =
+        // 8x^2 * cos(x) * exp(x) - 2x^4 * sin(x) * exp(x) + 2x^4 * cos(x) * exp(x)
+        let f1 = SingletonPolynomial::new_poly(TWO, FOUR);
+        let f2 = Trignometric::new_cosine(ONE);
+        let f3 = Exp::new();
+        let deriv = CF::Mul(
+            Box::new(CF::Func(BF::Poly(f1))),
+            Box::new(CF::Mul(
+                Box::new(CF::Func(BF::Trig(f2))),
+                Box::new(CF::Func(BF::Exp(f3))),
+            )),
+        )
+        .diff();
+        assert_about_eq!(deriv.evaluate(3.4), -14804.9016757);
+        assert_about_eq!(deriv.evaluate(0.07), 0.00298352866);
+
+        // Div
+        //
+        // (d/dx) (sin(x)/cos(x)) = (cos(x)*cos(x) + sin(x)*sin(x)) / cos(x)*cos(x)
+        let f1 = Trignometric::new_sine(ONE);
+        let f2 = Trignometric::new_cosine(ONE);
+        let deriv = CF::Div(
+            Box::new(CF::Func(BF::Trig(f1))),
+            Box::new(CF::Func(BF::Trig(f2))),
+        )
+        .diff();
+        assert_about_eq!(deriv.evaluate(core::f64::consts::PI), 1f64);
+        assert_about_eq!(deriv.evaluate(0f64), 1f64);
+
+        // Comp
+        //
+        // d/dx (cos(x^2)) = -2x * sin(x^2)
+        let f1 = Trignometric::new_cosine(ONE);
+        let f2 = SingletonPolynomial::new_poly(ONE, TWO);
+        let deriv = CF::Comp(
+            Box::new(CF::Func(BF::Trig(f1))),
+            Box::new(CF::Func(BF::Poly(f2))),
+        )
+        .diff();
+        assert_about_eq!(deriv.evaluate(2.714), -4.79392977);
+        assert_about_eq!(deriv.evaluate(3.9), -3.72556973);
+    }
+}
--- a/src/assignments/assignment07.rs
+++ b/src/assignments/assignment07.rs
@@ -1,29 +0,0 @@
-//! Assignment 7: Mastering advanced types (2/2).
-//!
-//! The primary goal of this assignment is to understand generics, traits, and lifetimes.
-//!
-//! You should fill out the `todo!()` placeholders in such a way that `/scripts/grade-07.sh` works fine.
-//! See `assignment07_grade.rs` and `/scripts/grade-07.sh` for the test script.
-
-struct FindIter<'s, T: Eq> {
-    query: &'s [T],
-    base: &'s [T],
-    curr: usize,
-}
-
-impl<T: Eq> Iterator for FindIter<'_, T> {
-    type Item = usize;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        todo!()
-    }
-}
-
-/// Returns an iterator over substring query indexes in the base.
-pub fn find<'s, T: Eq>(query: &'s [T], base: &'s [T]) -> impl 's + Iterator<Item = usize> {
-    FindIter {
-        query,
-        base,
-        curr: 0,
-    }
-}
--- a/src/assignments/assignment07/generator.rs
+++ b/src/assignments/assignment07/generator.rs
@@ -0,0 +1,36 @@
+//! Generators
+
+enum Yielded<T> {
+    Value(T),
+    Stop,
+}
+
+/// Generator
+///
+/// Reference:
+/// - [Python generator](https://python-reference.readthedocs.io/en/latest/docs/generator/)
+#[allow(missing_debug_implementations)]
+pub struct Generator<T, S> {
+    state: S,
+    f: fn(&mut S) -> Yielded<T>,
+}
+
+impl<T, S> Iterator for Generator<T, S> {
+    type Item = T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        todo!()
+    }
+}
+
+/// Returns a generator that yields fibonacci numbers.
+pub fn fib_generator(first: usize, second: usize) -> Generator<usize, (usize, usize)> {
+    todo!()
+}
+
+/// Returns a generator that yields collatz numbers.
+///
+/// The generator stops when it reaches to 1.
+pub fn collatz_conjecture(start: usize) -> Generator<usize, usize> {
+    todo!()
+}
--- a/src/assignments/assignment07/generator_grade.rs
+++ b/src/assignments/assignment07/generator_grade.rs
@@ -0,0 +1,38 @@
+#[cfg(test)]
+mod test {
+    use itertools::Itertools;
+    use ntest::assert_about_eq;
+
+    use super::super::generator::*;
+
+    #[test]
+    fn test_generator() {
+        assert_eq!(
+            fib_generator(0, 1).take(10).collect::<Vec<_>>(),
+            vec![0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
+        );
+
+        assert_eq!(
+            collatz_conjecture(12).collect::<Vec<_>>(),
+            vec![12, 6, 3, 10, 5, 16, 8, 4, 2, 1]
+        );
+
+        assert_eq!(
+            collatz_conjecture(19).collect::<Vec<_>>(),
+            vec![19, 58, 29, 88, 44, 22, 11, 34, 17, 52, 26, 13, 40, 20, 10, 5, 16, 8, 4, 2, 1]
+        );
+
+        assert_eq!(
+            collatz_conjecture(27).collect::<Vec<_>>(),
+            vec![
+                27, 82, 41, 124, 62, 31, 94, 47, 142, 71, 214, 107, 322, 161, 484, 242, 121, 364,
+                182, 91, 274, 137, 412, 206, 103, 310, 155, 466, 233, 700, 350, 175, 526, 263, 790,
+                395, 1186, 593, 1780, 890, 445, 1336, 668, 334, 167, 502, 251, 754, 377, 1132, 566,
+                283, 850, 425, 1276, 638, 319, 958, 479, 1438, 719, 2158, 1079, 3238, 1619, 4858,
+                2429, 7288, 3644, 1822, 911, 2734, 1367, 4102, 2051, 6154, 3077, 9232, 4616, 2308,
+                1154, 577, 1732, 866, 433, 1300, 650, 325, 976, 488, 244, 122, 61, 184, 92, 46, 23,
+                70, 35, 106, 53, 160, 80, 40, 20, 10, 5, 16, 8, 4, 2, 1
+            ]
+        );
+    }
+}
--- a/src/assignments/assignment07/hubo.rs
+++ b/src/assignments/assignment07/hubo.rs
@@ -0,0 +1,84 @@
+//! Hubo is back!
+
+/// Types that represent a direction.
+pub trait Direction {
+    /// Get the direction in the form of a 2-dimensional vector.
+    /// The resulting value doesn't have to be normalized.
+    fn get_vector(&self) -> (f32, f32);
+}
+
+/// 4-way enum to indicate directions.
+#[derive(Debug)]
+pub enum Dir4 {
+    /// +x direction
+    Right,
+    /// -x direction
+    Left,
+    /// +y direction
+    Up,
+    /// -y direction
+    Down,
+}
+
+impl Direction for Dir4 {
+    fn get_vector(&self) -> (f32, f32) {
+        todo!()
+    }
+}
+
+impl Direction for (f32, f32) {
+    fn get_vector(&self) -> (f32, f32) {
+        todo!()
+    }
+}
+
+/// Hubo.
+/// It's direction can be represented by an arbitrary type.
+///
+/// It can be controlled by [HuboController] only if the direction type implements the [Direction] trait.
+#[derive(Debug)]
+pub struct Hubo<TDir> {
+    direction: TDir,
+    x: f32,
+    y: f32,
+}
+
+/// Controller of the Hubo
+#[derive(Debug)]
+pub struct HuboController<'s, TDir> {
+    hubo: &'s mut Hubo<TDir>,
+}
+
+impl<TDir> Hubo<TDir> {
+    /// Create a Hubo.
+    pub fn new(direction: TDir, x: f32, y: f32) -> Self {
+        Self { direction, x, y }
+    }
+
+    /// Return the current position of Hubo.
+    pub fn get_position(&self) -> (f32, f32) {
+        (self.x, self.y)
+    }
+}
+
+impl<'s, TDir: Direction> HuboController<'s, TDir> {
+    /// Return the controller of the given Hubo.
+    /// Note that the lifetime of hubo's mutable reference \['s\] is repeated in the return type.
+    ///
+    /// This represents that the controller cannot live longer than the mutable reference,
+    /// since the controller takes and stores the reference.
+    pub fn new(hubo: &'s mut Hubo<TDir>) -> HuboController<'s, TDir> {
+        todo!()
+    }
+
+    /// Make Hubo move forward by the given distance. You might need to normalize the vector
+    /// acquired from `Direction::get_move_vector`.
+    pub fn move_hubo_forward(&mut self, distance: f32) {
+        todo!()
+    }
+
+    /// Make Hubo turn to the given direction.
+    pub fn set_hubo_direction(&mut self, dir: TDir) {
+        todo!()
+    }
+}
--- a/src/assignments/assignment07/hubo_grade.rs
+++ b/src/assignments/assignment07/hubo_grade.rs
@@ -0,0 +1,40 @@
+#[cfg(test)]
+mod test {
+    use itertools::Itertools;
+    use ntest::assert_about_eq;
+
+    use super::super::hubo::*;
+
+    #[test]
+    fn test_hubo_dir4_movement() {
+        let mut hubo = Hubo::new(Dir4::Right, 0.0, 0.0);
+        let mut controller = HuboController::new(&mut hubo);
+
+        // Test moving forward
+        controller.move_hubo_forward(5.0);
+
+        controller.set_hubo_direction(Dir4::Up);
+        controller.move_hubo_forward(3.0);
+
+        controller.set_hubo_direction(Dir4::Left);
+        controller.move_hubo_forward(2.0);
+
+        assert_eq!(hubo.get_position(), (3.0, 3.0));
+    }
+
+    #[test]
+    fn test_hubo_tuple_movement() {
+        let mut hubo = Hubo::new((1., 0.), 0.0, 0.0);
+        let mut controller = HuboController::new(&mut hubo);
+
+        // Test moving forward
+        controller.move_hubo_forward(5.0);
+
+        controller.set_hubo_direction((3., 4.));
+        controller.move_hubo_forward(5.0);
+
+        controller.set_hubo_direction((-8., -6.));
+        controller.move_hubo_forward(15.0);
+        assert_eq!(hubo.get_position(), (-4., -5.));
+    }
+}
--- a/src/assignments/assignment07/mod.rs
+++ b/src/assignments/assignment07/mod.rs
@@ -0,0 +1,18 @@
+//! Assignment 7: Mastering advanced types (2/2).
+//!
+//! The primary goal of this assignment is to understand generics, traits, and lifetimes.
+//!
+//! You should fill out the `todo!()` placeholders in such a way that `/scripts/grade-07.sh` works fine.
+//! See `assignment07_grade.rs` and `/scripts/grade-07.sh` for the test script.
+
+pub mod generator;
+pub mod hubo;
+pub mod my_itertools;
+pub mod small_exercises;
+pub mod transform;
+
+mod generator_grade;
+mod hubo_grade;
+mod my_itertools_grade;
+mod small_exercises_grade;
+mod transform_grade;
--- a/src/assignments/assignment07/my_itertools.rs
+++ b/src/assignments/assignment07/my_itertools.rs
@@ -0,0 +1,117 @@
+//! Implement your own minimal `itertools` crate.
+
+use std::hash::Hash;
+
+/// Iterator that iterates over the given iterator and returns only unique elements.
+#[allow(missing_debug_implementations)]
+pub struct Unique<I: Iterator> {
+    // TODO: remove `_marker` and add necessary fields as you want
+    _marker: std::marker::PhantomData<I>,
+}
+
+impl<I: Iterator> Iterator for Unique<I>
+where
+    I::Item: Eq + Hash + Clone,
+{
+    type Item = I::Item;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        todo!()
+    }
+}
+
+/// Iterator that chains two iterators together.
+#[allow(missing_debug_implementations)]
+pub struct Chain<I1: Iterator, I2: Iterator> {
+    // TODO: remove `_marker` and add necessary fields as you want
+    _marker: std::marker::PhantomData<(I1, I2)>,
+}
+
+impl<T: Eq + Hash + Clone, I1: Iterator<Item = T>, I2: Iterator<Item = T>> Iterator
+    for Chain<I1, I2>
+{
+    type Item = T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        todo!()
+    }
+}
+
+/// Iterator that iterates over given iterator and enumerates each element.
+#[allow(missing_debug_implementations)]
+pub struct Enumerate<I: Iterator> {
+    // TODO: remove `_marker` and add necessary fields as you want
+    _marker: std::marker::PhantomData<I>,
+}
+
+impl<I: Iterator> Iterator for Enumerate<I> {
+    type Item = (usize, I::Item);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        todo!()
+    }
+}
+
+/// Iterator that zips two iterators together.
+///
+/// If one iterator is longer than the other one, the remaining elements for the longer element
+/// should be ignored.
+#[allow(missing_debug_implementations)]
+pub struct Zip<I1: Iterator, I2: Iterator> {
+    // TODO: remove `_marker` and add necessary fields as you want
+    _marker: std::marker::PhantomData<(I1, I2)>,
+}
+
+impl<I1: Iterator, I2: Iterator> Iterator for Zip<I1, I2> {
+    type Item = (I1::Item, I2::Item);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        todo!()
+    }
+}
+
+/// My Itertools trait.
+pub trait MyIterTools: Iterator {
+    /// Returns an iterator that iterates over the `self` and returns only unique elements.
+    fn my_unique(self) -> Unique<Self>
+    where
+        Self: Sized,
+    {
+        todo!()
+    }
+
+    /// Returns an iterator that chains `self` and `other` together.
+    fn my_chain<I: Iterator>(self, other: I) -> Chain<Self, I>
+    where
+        Self: Sized,
+    {
+        todo!()
+    }
+
+    /// Returns an iterator that iterates over `self` and enumerates each element.
+    fn my_enumerate(self) -> Enumerate<Self>
+    where
+        Self: Sized,
+    {
+        todo!()
+    }
+
+    /// Returns an iterator that zips `self` and `other` together.
+    fn my_zip<I: Iterator>(self, other: I) -> Zip<Self, I>
+    where
+        Self: Sized,
+    {
+        todo!()
+    }
+
+    /// Foldleft for `MyIterTools`
+    fn my_fold<T, F>(mut self, init: T, mut f: F) -> T
+    where
+        Self: Sized,
+        F: FnMut(Self::Item, T) -> T,
+    {
+        todo!()
+    }
+}
+
+impl<T: ?Sized> MyIterTools for T where T: Iterator {}
--- a/src/assignments/assignment07/my_itertools_grade.rs
+++ b/src/assignments/assignment07/my_itertools_grade.rs
@@ -0,0 +1,65 @@
+#[cfg(test)]
+mod test {
+    use itertools::Itertools;
+    use ntest::assert_about_eq;
+
+    use super::super::my_itertools::*;
+
+    #[test]
+    fn test_itertools() {
+        assert_eq!(
+            [10, 1, 1, 1, 2, 3, 4, 1, 3, 2]
+                .into_iter()
+                .my_chain(std::iter::repeat(100))
+                .my_unique()
+                .take(4)
+                .collect::<Vec<_>>(),
+            vec![10, 1, 2, 3]
+        );
+
+        assert_eq!(
+            std::iter::repeat(5)
+                .my_enumerate()
+                .map(|(i, e)| { i * e })
+                .take(5)
+                .collect::<Vec<_>>(),
+            vec![0, 5, 10, 15, 20]
+        );
+
+        assert_eq!(
+            vec![0, 1, 10, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,],
+            [0, 1, 10].into_iter().my_chain(0..10).collect::<Vec<_>>(),
+        );
+
+        let it = || (1..=5).cycle().my_zip((1..=3).cycle()).map(|(x, y)| x * y);
+        let take15 = vec![
+            2,  // 1 * 1,
+            4,  // 2 * 2,
+            9,  // 3 * 3,
+            4,  // 4 * 1,
+            10, // 5 * 2,
+            3,  // 1 * 3,
+            2,  // 2 * 1,
+            6,  // 3 * 2,
+            12, // 4 * 3,
+            5,  // 5 * 1,
+            2,  // 1 * 2,
+            6,  // 2 * 3,
+            3,  // 3 * 1,
+            8,  // 4 * 2,
+            15, // 5 * 3,
+        ];
+
+        assert_eq!(
+            // 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5
+            // 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3
+            it().take(15).collect::<Vec<_>>(),
+            take15
+        );
+
+        assert_eq!(
+            it().take(15).my_fold(0, |elt, acc| elt + acc),
+            take15.iter().sum()
+        );
+    }
+}
--- a/src/assignments/assignment07/small_exercises.rs
+++ b/src/assignments/assignment07/small_exercises.rs
@@ -0,0 +1,119 @@
+//! Implement functions usint `Iterator` trait
+
+struct FindIter<'s, T: Eq> {
+    query: &'s [T],
+    base: &'s [T],
+    curr: usize,
+}
+
+impl<T: Eq> Iterator for FindIter<'_, T> {
+    type Item = usize;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        todo!()
+    }
+}
+
+/// Returns an iterator over substring query indexes in the base.
+pub fn find<'s, T: Eq>(query: &'s [T], base: &'s [T]) -> impl 's + Iterator<Item = usize> {
+    FindIter {
+        query,
+        base,
+        curr: 0,
+    }
+}
+
+/// Implement fibonacci iterator
+struct FibIter<T> {
+    // TODO: remove `_marker` and add necessary fields as you want
+    _marker: std::marker::PhantomData<T>,
+}
+
+impl<T: std::ops::Add<Output = T> + Copy> FibIter<T> {
+    fn new(first: T, second: T) -> Self {
+        todo!()
+    }
+}
+
+impl<T> Iterator for FibIter<T>
+where
+    T: std::ops::Add<Output = T> + Copy,
+{
+    type Item = T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        todo!()
+    }
+}
+
+/// Returns and iterator over the generic fibonacci sequence starting from `first` and `second`.
+/// This is a generic version of `fibonacci` function, which works for any types that implements `std::ops::Add` trait.
+pub fn fib<T>(first: T, second: T) -> impl Iterator<Item = T>
+where
+    T: std::ops::Add<Output = T> + Copy,
+{
+    todo!("remove below");
+    std::iter::empty()
+}
+
+/// Endpoint of range, inclusive or exclusive.
+#[derive(Debug)]
+pub enum Endpoint {
+    /// Inclusive endpoint
+    Inclusive(isize),
+
+    /// Exclusive endpoint
+    Exclusive(isize),
+}
+
+struct RangeIter {
+    // TODO: add necessary fields as you want
+}
+
+impl RangeIter {
+    fn new(endpoints: (Endpoint, Endpoint), step: isize) -> Self {
+        todo!()
+    }
+}
+
+impl Iterator for RangeIter {
+    type Item = isize;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        todo!()
+    }
+}
+
+/// Returns an iterator over the range [left, right) with the given step.
+pub fn range(left: Endpoint, right: Endpoint, step: isize) -> impl Iterator<Item = isize> {
+    todo!("remove below");
+    std::iter::empty()
+}
+
+/// Write an iterator that returns all divisors of n in increasing order.
+/// Assume n > 0.
+///
+/// Hint: trying all candidates from 1 to n will most likely time out!
+/// To optimize it, make use of the following fact:
+/// if x is a divisor of n that is greater than sqrt(n),
+/// then n/x is a divisor of n that is smaller than sqrt(n).
+struct Divisors {
+    n: u64,
+    // TODO: you may define additional fields here
+}
+
+impl Iterator for Divisors {
+    type Item = u64;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        todo!()
+    }
+}
+
+/// Returns an iterator over the divisors of n.
+pub fn divisors(n: u64) -> impl Iterator<Item = u64> {
+    Divisors {
+        n,
+        // TODO: you may define additional fields here
+    }
+}
--- a/src/assignments/assignment07/small_exercises_grade.rs
+++ b/src/assignments/assignment07/small_exercises_grade.rs
@@ -0,0 +1,189 @@
+#[cfg(test)]
+mod test {
+    use itertools::Itertools;
+    use ntest::assert_about_eq;
+
+    use super::super::small_exercises::*;
+
+    #[test]
+    fn test_find() {
+        assert_eq!(
+            find("abc".as_bytes(), "abcdabcd".as_bytes()).collect::<Vec<usize>>(),
+            vec![0, 4]
+        );
+
+        assert_eq!(
+            find("aaba".as_bytes(), "aabaacaadaabaaba".as_bytes()).collect::<Vec<usize>>(),
+            vec![0, 9, 12]
+        );
+
+        assert_eq!(
+            find("ababac".as_bytes(), "abababcabababcabababc".as_bytes()).collect::<Vec<usize>>(),
+            vec![]
+        );
+
+        assert_eq!(
+            find("ababc".as_bytes(), "abc".as_bytes()).collect::<Vec<usize>>(),
+            vec![]
+        );
+    }
+
+    #[test]
+    fn test_find_usize() {
+        assert_eq!(
+            find(&[1, 2, 3], &[1, 2, 3, 4, 1, 2, 3, 4]).collect::<Vec<usize>>(),
+            vec![0, 4]
+        );
+
+        assert_eq!(
+            find(
+                &[5, 5, 7, 5],
+                &[5, 5, 7, 5, 5, 8, 5, 5, 9, 5, 5, 7, 5, 5, 7, 5]
+            )
+            .collect::<Vec<usize>>(),
+            vec![0, 9, 12]
+        );
+    }
+
+    #[test]
+    fn test_fib_iter() {
+        assert_eq!(
+            fib(0, 1).take(10).collect::<Vec<_>>(),
+            vec![0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
+        );
+
+        #[derive(Debug, PartialEq, Eq, Clone, Copy)]
+        struct Rgb(u8, u8, u8);
+
+        impl std::ops::Add for Rgb {
+            type Output = Self;
+
+            fn add(self, rhs: Self) -> Self::Output {
+                Self(
+                    ((self.0 as u16 + rhs.0 as u16) / 2) as u8,
+                    ((self.1 as u16 + rhs.1 as u16) / 2) as u8,
+                    ((self.2 as u16 + rhs.2 as u16) / 2) as u8,
+                )
+            }
+        }
+
+        assert_eq!(
+            fib(Rgb(255, 0, 100), Rgb(1, 128, 0))
+                .take(20)
+                .collect::<Vec<_>>(),
+            vec![
+                Rgb(255, 0, 100),
+                Rgb(1, 128, 0),
+                Rgb(128, 64, 50),
+                Rgb(64, 96, 25),
+                Rgb(96, 80, 37),
+                Rgb(80, 88, 31),
+                Rgb(88, 84, 34),
+                Rgb(84, 86, 32),
+                Rgb(86, 85, 33),
+                Rgb(85, 85, 32),
+                Rgb(85, 85, 32),
+                Rgb(85, 85, 32),
+                Rgb(85, 85, 32),
+                Rgb(85, 85, 32),
+                Rgb(85, 85, 32),
+                Rgb(85, 85, 32),
+                Rgb(85, 85, 32),
+                Rgb(85, 85, 32),
+                Rgb(85, 85, 32),
+                Rgb(85, 85, 32)
+            ]
+        );
+    }
+
+    #[test]
+    fn test_range_iter() {
+        let one_to_tens = vec![
+            vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10],
+            range(Endpoint::Inclusive(1), Endpoint::Inclusive(10), 1).collect(),
+            range(Endpoint::Exclusive(0), Endpoint::Inclusive(10), 1).collect(),
+            range(Endpoint::Inclusive(1), Endpoint::Exclusive(11), 1).collect(),
+            range(Endpoint::Exclusive(0), Endpoint::Exclusive(11), 1).collect(),
+        ];
+        assert!(one_to_tens.iter().all_equal());
+
+        let ten_to_ones = vec![
+            vec![10, 9, 8, 7, 6, 5, 4, 3, 2, 1],
+            range(Endpoint::Inclusive(10), Endpoint::Inclusive(1), -1).collect(),
+            range(Endpoint::Exclusive(11), Endpoint::Inclusive(1), -1).collect(),
+            range(Endpoint::Inclusive(10), Endpoint::Exclusive(0), -1).collect(),
+            range(Endpoint::Exclusive(11), Endpoint::Exclusive(0), -1).collect(),
+        ];
+        assert!(ten_to_ones.iter().all_equal());
+
+        let five_evens = vec![
+            vec![2, 4, 6, 8, 10],
+            range(Endpoint::Inclusive(2), Endpoint::Inclusive(10), 2).collect(),
+            range(Endpoint::Inclusive(2), Endpoint::Inclusive(11), 2).collect(),
+            range(Endpoint::Exclusive(1), Endpoint::Inclusive(10), 2).collect(),
+            range(Endpoint::Exclusive(1), Endpoint::Inclusive(11), 2).collect(),
+            range(Endpoint::Inclusive(2), Endpoint::Exclusive(11), 2).collect(),
+            range(Endpoint::Inclusive(2), Endpoint::Exclusive(12), 2).collect(),
+            range(Endpoint::Exclusive(1), Endpoint::Exclusive(11), 2).collect(),
+            range(Endpoint::Exclusive(1), Endpoint::Exclusive(12), 2).collect(),
+        ];
+        assert!(five_evens.iter().all_equal());
+
+        let emptys = vec![
+            vec![],
+            range(Endpoint::Inclusive(2), Endpoint::Inclusive(10), -1).collect(),
+            range(Endpoint::Inclusive(10), Endpoint::Inclusive(-100), 1).collect(),
+            range(Endpoint::Inclusive(1), Endpoint::Exclusive(1), 1).collect(),
+        ];
+        assert!(emptys.iter().all_equal());
+    }
+
+    #[test]
+    fn test_small() {
+        assert_eq!(divisors(10).collect::<Vec<u64>>(), vec![1, 2, 5, 10]);
+
+        assert_eq!(divisors(17).collect::<Vec<u64>>(), vec![1, 17]);
+
+        assert_eq!(divisors(49).collect::<Vec<u64>>(), vec![1, 7, 49]);
+
+        assert_eq!(
+            divisors(120).collect::<Vec<u64>>(),
+            vec![1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 20, 24, 30, 40, 60, 120]
+        );
+
+        assert_eq!(divisors(1).collect::<Vec<u64>>(), vec![1]);
+
+        assert_eq!(divisors(2).collect::<Vec<u64>>(), vec![1, 2]);
+
+        assert_eq!(divisors(3).collect::<Vec<u64>>(), vec![1, 3]);
+    }
+
+    #[test]
+    fn test_large() {
+        assert_eq!(
+            divisors(1_000_000_000_000_037).collect::<Vec<u64>>(),
+            vec![1, 1_000_000_000_000_037]
+        );
+
+        assert_eq!(
+            divisors(99_999_820_000_081).collect::<Vec<u64>>(),
+            vec![1, 9_999_991, 99_999_820_000_081]
+        );
+
+        assert_eq!(
+            divisors(1_234_567_890_123).collect::<Vec<u64>>(),
+            vec![
+                1,
+                3,
+                3_541,
+                10_623,
+                116_216_501,
+                348_649_503,
+                411_522_630_041,
+                1_234_567_890_123
+            ]
+        );
+
+        assert_eq!(divisors(97_821_761_637_600).count(), 17280);
+    }
+}
--- a/src/assignments/assignment07/transform.rs
+++ b/src/assignments/assignment07/transform.rs
@@ -0,0 +1,95 @@
+//! Tranformer
+use std::marker::PhantomData;
+use std::ops::Add;
+
+/// Represents transformation of type `T`.
+pub trait Transform<T> {
+    /// Transforms value.
+    fn transform(&self, value: T) -> T;
+}
+
+impl<T1, T2, Tr1: Transform<T1>, Tr2: Transform<T2>> Transform<(T1, T2)> for (Tr1, Tr2) {
+    fn transform(&self, value: (T1, T2)) -> (T1, T2) {
+        todo!()
+    }
+}
+
+/// Identity transformation.
+#[derive(Debug, Clone, Copy)]
+pub struct Identity;
+
+impl<T> Transform<T> for Identity {
+    fn transform(&self, value: T) -> T {
+        todo!()
+    }
+}
+
+/// Custom transformation.
+#[derive(Debug, Clone, Copy)]
+pub struct Custom<T, F: Fn(T) -> T> {
+    f: F,
+    _marker: PhantomData<T>,
+}
+
+impl<T, F: Fn(T) -> T> From<F> for Custom<T, F> {
+    fn from(f: F) -> Self {
+        Self {
+            f,
+            _marker: PhantomData,
+        }
+    }
+}
+
+impl<T, F: Fn(T) -> T> Transform<T> for Custom<T, F> {
+    fn transform(&self, value: T) -> T {
+        todo!()
+    }
+}
+
+/// Repeats transformation for `n` times.
+#[derive(Debug, Clone, Copy)]
+pub struct Repeat<T, Tr: Transform<T>> {
+    inner: Tr,
+    n: u32,
+    _marker: PhantomData<T>,
+}
+
+impl<T, Tr: Transform<T>> Repeat<T, Tr> {
+    /// Creates a new repeat transformation.
+    pub fn new(inner: Tr, n: u32) -> Self {
+        Repeat {
+            inner,
+            n,
+            _marker: PhantomData,
+        }
+    }
+}
+
+impl<T, Tr: Transform<T>> Transform<T> for Repeat<T, Tr> {
+    fn transform(&self, mut value: T) -> T {
+        todo!()
+    }
+}
+
+/// Repeats transformation until converges.
+#[derive(Debug, Clone, Copy)]
+pub struct RepeatUntilConverge<T: Eq, Tr: Transform<T>> {
+    inner: Tr,
+    _marker: PhantomData<T>,
+}
+
+impl<T: Clone + Eq, Tr: Transform<T>> RepeatUntilConverge<T, Tr> {
+    /// Creates a new repeat transformation.
+    pub fn new(inner: Tr) -> Self {
+        RepeatUntilConverge {
+            inner,
+            _marker: PhantomData,
+        }
+    }
+}
+
+impl<T: Clone + Eq, Tr: Transform<T>> Transform<T> for RepeatUntilConverge<T, Tr> {
+    fn transform(&self, mut value: T) -> T {
+        todo!()
+    }
+}
--- a/src/assignments/assignment07/transform_grade.rs
+++ b/src/assignments/assignment07/transform_grade.rs
@@ -0,0 +1,62 @@
+#[cfg(test)]
+mod test {
+    use itertools::Itertools;
+    use ntest::assert_about_eq;
+
+    use super::super::transform::*;
+
+    #[test]
+    fn test_transform_identity() {
+        let tr = Identity;
+
+        assert_eq!(tr.transform(3), 3);
+        assert_eq!(tr.transform(3.0), 3.0);
+        assert_eq!(tr.transform("abc"), "abc");
+    }
+
+    #[test]
+    fn test_transform_tuple() {
+        let f1 = |x: u32| x + 1;
+        let f2 = |x: String| x.clone() + &x;
+
+        let tr1: Custom<_, _> = f1.into();
+        let tr2: Custom<_, _> = f2.into();
+
+        let list1 = 0u32..10u32;
+        let list2 = ["a".to_string(), "bb".to_string(), "ccc".to_string()];
+
+        for v1 in list1 {
+            for v2 in list2.clone() {
+                let tr = (tr1, tr2.clone());
+                let input = (v1, v2.clone());
+                let expected = (f1(v1), f2(v2));
+                assert_eq!(tr.transform(input), expected);
+            }
+        }
+    }
+
+    #[test]
+    fn test_transform_repeat() {
+        let inc = Custom::from(|x: i32| x + 1);
+        let dec = Custom::from(|x: i32| x - 1);
+
+        for i in 0..10 {
+            for j in -10..10 {
+                assert_eq!(Repeat::new(inc, i as u32).transform(j), j + i);
+                assert_eq!(Repeat::new(dec, i as u32).transform(j), j - i);
+            }
+        }
+    }
+
+    #[test]
+    fn test_transform_repeat_until_converge() {
+        let inc = Custom::from(|x: i32| if x < 50 { x + 1 } else { x });
+        let dec = Custom::from(|x: i32| if x > 50 { x - 1 } else { x });
+
+        assert_eq!(RepeatUntilConverge::new(inc).transform(40), 50);
+        assert_eq!(RepeatUntilConverge::new(inc).transform(60), 60);
+
+        assert_eq!(RepeatUntilConverge::new(dec).transform(40), 40);
+        assert_eq!(RepeatUntilConverge::new(dec).transform(60), 50);
+    }
+}
--- a/src/assignments/assignment07_grade.rs
+++ b/src/assignments/assignment07_grade.rs
@@ -1,44 +0,0 @@
-#[cfg(test)]
-mod test {
-    use super::super::assignment07::*;
-
-    #[test]
-    fn test_find() {
-        assert_eq!(
-            find("abc".as_bytes(), "abcdabcd".as_bytes()).collect::<Vec<usize>>(),
-            vec![0, 4]
-        );
-
-        assert_eq!(
-            find("aaba".as_bytes(), "aabaacaadaabaaba".as_bytes()).collect::<Vec<usize>>(),
-            vec![0, 9, 12]
-        );
-
-        assert_eq!(
-            find("ababac".as_bytes(), "abababcabababcabababc".as_bytes()).collect::<Vec<usize>>(),
-            vec![]
-        );
-
-        assert_eq!(
-            find("ababc".as_bytes(), "abc".as_bytes()).collect::<Vec<usize>>(),
-            vec![]
-        );
-    }
-
-    #[test]
-    fn test_find_usize() {
-        assert_eq!(
-            find(&[1, 2, 3], &[1, 2, 3, 4, 1, 2, 3, 4]).collect::<Vec<usize>>(),
-            vec![0, 4]
-        );
-
-        assert_eq!(
-            find(
-                &[5, 5, 7, 5],
-                &[5, 5, 7, 5, 5, 8, 5, 5, 9, 5, 5, 7, 5, 5, 7, 5]
-            )
-            .collect::<Vec<usize>>(),
-            vec![0, 9, 12]
-        );
-    }
-}
--- a/src/assignments/assignment09/bigint.rs
+++ b/src/assignments/assignment09/bigint.rs
@@ -0,0 +1,94 @@
+//! Big integer with infinite precision.
+
+use std::fmt;
+use std::{iter::zip, ops::*};
+
+/// An signed integer with infinite precision implemented with an "carrier" vector of `u32`s.
+///
+/// The vector is interpreted as a base 2^(32 * (len(carrier) - 1)) integer, where negative
+/// integers are represented in their [2's complement form](https://en.wikipedia.org/wiki/Two%27s_complement).
+///
+/// For example, the vector `vec![44,345,3]` represents the integer
+/// `44 * (2^32)^2 + 345 * (2^32) + 3`,
+/// and the vector `vec![u32::MAX - 5, u32::MAX - 7]` represents the integer
+/// `- (5 * 2^32 + 8)
+///
+/// You will implement the `Add` and `Sub` trait for this type.
+///
+/// Unlike standard fix-sized intergers in Rust where overflow will panic, the carrier is extended to save the overflowed bit.
+/// On the contrary, if the precision is too much (e.g, vec![0,0] is used to represent 0, where `vec![0]` is sufficent), the carrier is truncated.
+///
+/// See [this section](https://en.wikipedia.org/wiki/Two%27s_complement#Arithmetic_operations) for a rouge guide on implementation,
+/// while keeping in mind that the carrier should be extended to deal with overflow.
+///
+/// The `sign_extension()`, `two_complement()`, and `truncate()` are non-mandatory helper methods.
+///
+/// For testing and debugging pruposes, the `Display` trait is implemented for you, which shows the integer in hexadecimal form.
+#[derive(Debug, Clone)]
+pub struct BigInt {
+    /// The carrier for `BigInt`.
+    ///
+    /// Note that the carrier should always be non-empty.
+    pub carrier: Vec<u32>,
+}
+
+impl BigInt {
+    /// Create a new `BigInt` from a `usize`.
+    pub fn new(n: u32) -> Self {
+        todo!()
+    }
+
+    /// Creates a new `BigInt` from a `Vec<u32>`.
+    ///
+    /// # Panic
+    ///
+    /// Panics if `carrier` is empty.
+    pub fn new_large(carrier: Vec<u32>) -> Self {
+        todo!()
+    }
+}
+
+const SIGN_MASK: u32 = 1 << 31;
+
+impl BigInt {
+    /// Extend `self` to `len` bits.
+    fn sign_extension(&self, len: usize) -> Self {
+        todo!()
+    }
+
+    /// Compute the two's complement of `self`.
+    fn two_complement(&self) -> Self {
+        todo!()
+    }
+
+    /// Truncate a `BigInt` to the minimum length.
+    fn truncate(&self) -> Self {
+        todo!()
+    }
+}
+
+impl Add for BigInt {
+    type Output = Self;
+
+    fn add(self, rhs: Self) -> Self::Output {
+        todo!()
+    }
+}
+
+impl Sub for BigInt {
+    type Output = Self;
+
+    fn sub(self, rhs: Self) -> Self::Output {
+        todo!()
+    }
+}
+
+impl fmt::Display for BigInt {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        // Hex formatting so that each u32 can be formatted independently.
+        for i in self.carrier.iter() {
+            write!(f, "{:08x}", i)?;
+        }
+        Ok(())
+    }
+}
--- a/src/assignments/assignment09/bigint_grade.rs
+++ b/src/assignments/assignment09/bigint_grade.rs
@@ -0,0 +1,104 @@
+#[cfg(test)]
+mod test {
+
+    use ntest::{assert_false, assert_true};
+
+    use super::super::bigint::*;
+
+    #[test]
+    fn test_inf_prec_simple() {
+        // Basic
+        assert_eq!("00000000", format!("{}", BigInt::new(0)));
+        assert_eq!("ffffffff", format!("{}", BigInt::new(u32::MAX)));
+        assert_eq!("00bc4fdc", format!("{}", BigInt::new(12_341_212)));
+        assert_eq!("fffffed8", format!("{}", BigInt::new(4_294_967_000u32)));
+
+        // Add Basic
+        assert_eq!("00000001", format!("{}", BigInt::new(0) + BigInt::new(1)));
+
+        assert_eq!(
+            "0df655df",
+            format!("{}", BigInt::new(13_413) + BigInt::new(234_234_234))
+        );
+
+        assert_eq!(
+            "ffffff03",
+            format!("{}", BigInt::new(4_294_967_000u32) + BigInt::new(43))
+        );
+
+        // Sub Basic
+        assert_eq!("ffffffff", format!("{}", BigInt::new(0) - BigInt::new(1)));
+
+        assert_eq!(
+            "f20a12eb",
+            format!("{}", BigInt::new(13_413) - BigInt::new(234_234_234))
+        );
+
+        assert_eq!(
+            "fffffead",
+            format!("{}", BigInt::new(4_294_967_000u32) - BigInt::new(43))
+        );
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_inf_prec_panic() {
+        let _ = BigInt::new_large(vec![]);
+    }
+
+    #[test]
+    fn test_inf_prec_complex() {
+        // Positive overflow
+        assert_eq!(
+            "0000000080000000",
+            format!("{}", BigInt::new(i32::MAX as u32) + BigInt::new(1))
+        );
+
+        // Negative overflow
+        assert_eq!(
+            "ffffffff7fffffff",
+            format!("{}", BigInt::new(i32::MIN as u32) - BigInt::new(1))
+        );
+
+        // Larger positive overflow
+        assert_eq!(
+            "00000000fffffffe00000000",
+            format!(
+                "{}",
+                BigInt::new_large(vec![i32::MAX as u32, 0])
+                    + BigInt::new_large(vec![i32::MAX as u32, 0])
+            )
+        );
+
+        // Smaller negative overflow
+        assert_eq!(
+            "ffffffff000000000119464a",
+            format!(
+                "{}",
+                BigInt::new_large(vec![i32::MIN as u32, 2_871_572])
+                    + BigInt::new_large(vec![i32::MIN as u32, 15_562_038])
+            )
+        );
+
+        // Truncate
+        assert_eq!(
+            "00000000",
+            format!(
+                "{}",
+                BigInt::new_large(vec![i32::MIN as u32, 2_871_572, 123_456])
+                    - BigInt::new_large(vec![i32::MIN as u32, 2_871_572, 123_456])
+            )
+        );
+
+        assert_eq!(
+            "ffffffff",
+            format!(
+                "{}",
+                BigInt::new_large(vec![i32::MIN as u32, 2_871_572, 123_456])
+                    - BigInt::new_large(vec![i32::MIN as u32, 2_871_572, 123_457])
+            )
+        );
+
+        // TODO: add a test case testing sign extension.
+    }
+}
--- a/src/assignments/assignment09/mod.rs
+++ b/src/assignments/assignment09/mod.rs
@@ -0,0 +1,12 @@
+//! Assignment 9: Iterators (1/2).
+//!
+//! The primary goal of this assignment is to get used to iterators.
+//!
+//! You should fill out the `todo!()` placeholders in such a way that `/scripts/grade-09.sh` works fine.
+//! See `assignment09_grade.rs` and `/scripts/grade-09.sh` for the test script.
+
+pub mod bigint;
+pub mod small_exercises;
+
+mod bigint_grade;
+mod small_exercises_grade;
--- a/src/assignments/assignment09/small_exercises.rs
+++ b/src/assignments/assignment09/small_exercises.rs
@@ -1,14 +1,7 @@
-//! Assignment 9: Iterators (1/2).
-//!
-//! The primary goal of this assignment is to get used to iterators.
-//!
-//! You should fill out the `todo!()` placeholders in such a way that `/scripts/grade-09.sh` works fine.
-//! See `assignment09_grade.rs` and `/scripts/grade-09.sh` for the test script.
+//! Small exercises.

 use std::collections::HashMap;

-use itertools::*;
-
 /// Returns whether the given sequence is a fibonacci sequence starts from the given sequence's first two terms.
 ///
 /// Returns `true` if the length of sequence is less or equal than 2.
@@ -61,6 +54,27 @@ pub fn interleave3<T>(
    todo!()
 }

+/// Alternate elements from array of n iterators until they have run out.
+///
+/// You can assume that the number of elements of iterators are same.
+///
+/// # Example
+///
+/// ```
+/// use cs220::assignments::assignment09::interleave_n;
+///
+/// assert_eq!(
+///     interleave_n(&mut [[1, 2].into_iter(), [3, 4].into_iter(), [5, 6].into_iter()]),
+///     vec![1, 3, 5, 2, 4, 6]
+/// );
+/// ```
+pub fn interleave_n<T, const N: usize>(
+    mut iters: [impl Iterator<Item = T>; N],
+) -> impl Iterator<Item = T> {
+    todo!();
+    std::iter::empty()
+}
+
 /// Returns mean of k smallest value's mean.
 ///
 /// # Example
@@ -172,3 +186,26 @@ pub fn find_count_n(inner: Vec<usize>, n: usize) -> Vec<usize> {
 pub fn position_median<T: Ord>(inner: Vec<T>) -> Option<usize> {
    todo!()
 }
+
+/// Returns the sum of all elements in a two-dimensional array.
+///
+/// # Example
+/// ```
+/// assert_eq!(
+///     two_dimensional_sum([[1, 2, 3].into_iter(), [4, 5, 6].into_iter()].into_iter()),
+///     21
+/// );
+/// ```
+pub fn two_dimensional_sum(inner: impl Iterator<Item = impl Iterator<Item = i64>>) -> i64 {
+    todo!()
+}
+
+/// Returns whether the given string is palindrome or not.
+///
+/// A palindrome is a word, number, phrase, or other sequence of characters which reads the same backward as forward.
+/// We consider the empty string is palindrome.
+///
+/// Consult <https://en.wikipedia.org/wiki/Palindrome>.
+pub fn is_palindrome(s: String) -> bool {
+    todo!()
+}
--- a/src/assignments/assignment09/small_exercises_grade.rs
+++ b/src/assignments/assignment09/small_exercises_grade.rs
@@ -1,6 +1,9 @@
 #[cfg(test)]
 mod test {
-    use super::super::assignment09::*;
+
+    use ntest::{assert_false, assert_true};
+
+    use super::super::small_exercises::*;

    #[test]
    fn test_is_fibonacci() {
@@ -74,6 +77,35 @@ mod test {
        );
    }

+    #[test]
+    fn test_interleave_n() {
+        assert_eq!(
+            interleave_n([[1, 2].into_iter(), [3, 4].into_iter(), [5, 6].into_iter()])
+                .collect::<Vec<_>>(),
+            vec![1, 3, 5, 2, 4, 6]
+        );
+
+        assert_eq!(
+            interleave_n([
+                [1, 2, 3].into_iter(),
+                [4, 5, 6].into_iter(),
+                [7, 8, 9].into_iter()
+            ])
+            .collect::<Vec<_>>(),
+            vec![1, 4, 7, 2, 5, 8, 3, 6, 9]
+        );
+
+        assert_eq!(
+            interleave_n([
+                ["a", "b", "c"].into_iter(),
+                ["d", "e", "f"].into_iter(),
+                ["g", "h", "i"].into_iter()
+            ])
+            .collect::<String>(),
+            "adgbehcfi"
+        );
+    }
+
    #[test]
    fn test_k_smallest_man() {
        assert_eq!(
@@ -200,4 +232,37 @@ mod test {
        assert_eq!(position_median(vec![1, 3, 3, 6, 7, 8, 9]), Some(3));
        assert_eq!(position_median(vec![1, 2, 3, 4, 5, 6, 8, 9]), Some(4));
    }
+
+    #[test]
+    fn test_two_dimensional_sum() {
+        assert_eq!(
+            two_dimensional_sum([[1, 2, 3].into_iter(), [4, 5, 6].into_iter()].into_iter()),
+            21
+        );
+        assert_eq!(
+            two_dimensional_sum(
+                [
+                    [1, 2, 3, 4, 5].into_iter(),
+                    [10, 20, 30, 40, 50].into_iter()
+                ]
+                .into_iter()
+            ),
+            165
+        );
+    }
+
+    #[test]
+    fn test_is_palindrome() {
+        assert_true!(is_palindrome("kayak".to_string()));
+        assert_true!(is_palindrome("dammitimmad".to_string()));
+        assert_true!(is_palindrome("deified".to_string()));
+        assert_true!(is_palindrome("rotator".to_string()));
+        assert_true!(is_palindrome("noon".to_string()));
+        assert_true!(is_palindrome("".to_string()));
+        assert_true!(is_palindrome("a".to_string()));
+
+        assert_false!(is_palindrome("moon".to_string()));
+        assert_false!(is_palindrome("hello".to_string()));
+        assert_false!(is_palindrome("apple".to_string()));
+    }
 }
--- a/src/assignments/assignment10/labyrinth.rs
+++ b/src/assignments/assignment10/labyrinth.rs
@@ -0,0 +1,50 @@
+//! Labyrinth
+//!
+//! Look at the [test code](labyrinth_grade.rs) below before you start.
+//! HINT: https://en.wikipedia.org/wiki/100_prisoners_problem
+//!
+//! NOTE: You will have to implement a probabilistic algorithm, which means, the algorithm can fail
+//! even if you have implemented the solution. We recommend running multiple times (at least 5 times) to check your
+//! solution works well.
+
+#![allow(missing_docs)]
+
+use std::cell::RefCell;
+
+/// Husband
+#[derive(Debug)]
+pub struct Husband {
+    brain: RefCell<[usize; 100]>,
+}
+
+impl Husband {
+    /// What might a husband, who is looking for his wife's ID my_wife, be thinking?
+    pub fn seeking(my_wife: usize) -> Self {
+        todo!()
+    }
+
+    #[allow(missing_docs)]
+    pub fn has_devised_a_strategy(&self) -> Strategy<'_> {
+        Strategy { husband: self }
+    }
+
+    /// Based on the information about currently visited room number and someone's wife ID trapped inside,
+    /// what the husband should do next?
+    pub fn carefully_checks_whos_inside(&self, room: usize, wife: usize) {
+        todo!()
+    }
+}
+
+/// Strategy of husband
+#[derive(Debug)]
+pub struct Strategy<'a> {
+    husband: &'a Husband,
+}
+
+impl Iterator for Strategy<'_> {
+    type Item = usize;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        todo!()
+    }
+}
--- a/src/assignments/assignment10/labyrinth_grade.rs
+++ b/src/assignments/assignment10/labyrinth_grade.rs
@@ -0,0 +1,62 @@
+#[cfg(test)]
+mod test {
+    use rand::seq::SliceRandom;
+    use rand::thread_rng;
+
+    use super::super::labyrinth::*;
+
+    type Wife = usize;
+    type Rooms = Vec<Wife>;
+
+    struct Labyrinth {
+        rooms: Rooms,
+    }
+
+    impl From<Rooms> for Labyrinth {
+        fn from(rooms: Rooms) -> Self {
+            Self { rooms }
+        }
+    }
+
+    impl Labyrinth {
+        fn open_the_door(&self, index: usize) -> Wife {
+            self.rooms[index]
+        }
+    }
+
+    #[test]
+    fn can_every_husband_rescue_his_wife() {
+        // HINT: https://en.wikipedia.org/wiki/100_prisoners_problem
+        const WIVES: usize = 100;
+
+        // One day, wives of 100 husbands were kidnapped by the Minotaur
+        // and imprisoned in a labyrinth.... 🏰
+        let labyrinth = Labyrinth::from({
+            let mut rooms: Vec<_> = (0..WIVES).collect();
+            rooms.shuffle(&mut thread_rng());
+            rooms
+        });
+
+        assert!((0..WIVES).all(|his_wife| {
+            // A new husband steps into the labyrinth to rescue his wife...!
+            let husband = Box::new(Husband::seeking(his_wife /*👩*/));
+            let strategy = Box::new(husband.has_devised_a_strategy());
+
+            #[allow(clippy::all)]
+            /* The Minotaur🐂 will arrive in */
+            (0..50) /* steps... */
+                .zip(strategy)
+                .find(|(_, room)| {
+                    // The husband contemplates his next move... 🤔
+                    // and finally,
+                    let someone/*👤*/ = labyrinth.open_the_door(*room); // 🚪
+                    husband.carefully_checks_whos_inside(*room, someone);
+
+                    // Has the husband found his wife...?
+                    someone/*👤*/ == his_wife /*👩*/
+                })
+                .is_some(/* The husband has successfully rescued his wife! 👫*/)
+            // or is_none(/* The unfortunate husband has encountered the Minotaur and... 🪓*/)
+        }));
+    }
+}
--- a/src/assignments/assignment10/mod.rs
+++ b/src/assignments/assignment10/mod.rs
@@ -0,0 +1,12 @@
+//!
+//! Assignment 10: Iterators (2/2).
+//! The primary goal of this assignment is to get used to iterators.
+//!
+//! You should fill out the `todo!()` placeholders in such a way that `/scripts/grade-10.sh` works fine.
+//! See `assignment10_grade.rs` and `/scripts/grade-10.sh` for the test script.
+
+pub mod labyrinth;
+pub mod small_exercises;
+
+mod labyrinth_grade;
+mod small_exercises_grade;
--- a/src/assignments/assignment10/small_exercises.rs
+++ b/src/assignments/assignment10/small_exercises.rs
@@ -1,10 +1,4 @@
-//! Assignment 10: Iterators (2/2).
-//!
-//! The primary goal of this assignment is to get used to iterators.
-//!
-//! You should fill out the `todo!()` placeholders in such a way that `/scripts/grade-10.sh` works fine.
-//! See `assignment10_grade.rs` and `/scripts/grade-10.sh` for the test script.
-
+//! Small exercises.
 use itertools::*;

 /// Returns the pairs of `(i, j)` where `i < j` and `inner[i] > inner[j]` in increasing order.
@@ -117,3 +111,83 @@ pub enum File {
 pub fn du_sort(root: &File) -> Vec<(&str, usize)> {
    todo!()
 }
+
+/// Remove all even numbers inside a vector using the given mutable reference.
+/// That is, you must modify the vector using the given mutable reference instead
+/// of returning a new vector.
+///
+/// # Example
+/// ```
+/// let mut vec = vec![1, 2, 3, 4, 5];
+/// remove_even(&mut vec);
+/// assert_eq!(*vec, vec![1, 3, 5]);
+/// ```
+#[allow(clippy::ptr_arg)]
+pub fn remove_even(inner: &mut Vec<i64>) {
+    todo!()
+}
+
+/// Remove all duplicate occurences of a number inside the array.
+/// That is, if an integer appears more than once, remove some occurences
+/// of it so that it only appears once. Note that you must modify the vector
+/// using the given mutable reference instead of returning a new vector.
+/// Also, note that the order does not matter.
+///
+/// # Example
+/// ```
+/// let mut vec = vec![1, 2, 1, 1, 3, 7, 5, 7];
+/// remove_duplicate(&mut vec);
+/// assert_eq!(*vec, vec![1, 2, 3, 7, 5]);
+/// ```
+#[allow(clippy::ptr_arg)]
+pub fn remove_duplicate(inner: &mut Vec<i64>) {
+    todo!()
+}
+
+/// Returns the natural join of two tables using the first column as the join argument.
+/// That is, for each pair of a row(`Vec<String>`) from table1 and a row(`Vec<String>`) from table2,
+/// if the first element of them are equal, then add all elements of the row from table2
+/// except its first element to the row from table1 and add it to the results.
+/// Note that the order of results does not matter.
+///
+/// # Example
+///
+///        table1                     table2
+/// ----------------------     ----------------------
+///  20230001 |    Jack         20230001 |    CS
+///  20231234 |    Mike         20230001 |    EE
+///                             20231234 |    ME
+///
+///
+///               result
+/// -----------------------------------
+///  20230001 |    Jack   |     CS
+///  20230001 |    Jack   |     EE
+///  20231234 |    Mike   |     ME
+///
+pub fn natural_join(table1: Vec<Vec<String>>, table2: Vec<Vec<String>>) -> Vec<Vec<String>> {
+    todo!()
+}
+
+struct Pythagorean;
+
+impl Pythagorean {
+    fn new() -> Self {
+        todo!()
+    }
+}
+
+impl Iterator for Pythagorean {
+    type Item = (u64, u64, u64);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        todo!()
+    }
+}
+
+/// Generates sequence of unique [primitive Pythagorean
+/// triples](https://en.wikipedia.org/wiki/Pythagorean_triple), i.e. (a,b,c) such that a² + b² =
+/// c², a and b are coprimes, and a < b. Generate in the increasing order of c.
+pub fn pythagorean() -> impl Iterator<Item = (u64, u64, u64)> {
+    Pythagorean::new()
+}
--- a/src/assignments/assignment10/small_exercises_grade.rs
+++ b/src/assignments/assignment10/small_exercises_grade.rs
@@ -0,0 +1,351 @@
+#[cfg(test)]
+mod test {
+    use std::collections::HashSet;
+
+    use super::super::small_exercises::*;
+
+    #[test]
+    fn test_inversion() {
+        assert_eq!(inversion(vec![3, 5, 4]), vec![(1, 2)]);
+        assert_eq!(inversion(vec!["c", "a", "b", "d"]), vec![(0, 1), (0, 2)]);
+        assert_eq!(
+            inversion(vec![2, 5, 4, 6, 3, 1]),
+            vec![
+                (0, 5),
+                (1, 2),
+                (1, 4),
+                (1, 5),
+                (2, 4),
+                (2, 5),
+                (3, 4),
+                (3, 5),
+                (4, 5)
+            ]
+        );
+    }
+
+    #[test]
+    fn test_traverse_preorder() {
+        let root = Node::NonLeaf((
+            1,
+            vec![
+                Node::NonLeaf((2, vec![Node::Leaf(5), Node::Leaf(6)])),
+                Node::Leaf(3),
+                Node::NonLeaf((4, vec![Node::Leaf(7), Node::Leaf(8), Node::Leaf(9)])),
+            ],
+        ));
+
+        assert_eq!(traverse_preorder(root), vec![1, 2, 5, 6, 3, 4, 7, 8, 9]);
+    }
+
+    #[test]
+    fn test_du_sort() {
+        let rootfile = File::Directory(
+            "root".to_string(),
+            vec![
+                File::Directory(
+                    "a".to_string(),
+                    vec![
+                        File::Data("a1".to_string(), 1),
+                        File::Data("a2".to_string(), 3),
+                    ],
+                ),
+                File::Directory(
+                    "b".to_string(),
+                    vec![
+                        File::Data("b1".to_string(), 3),
+                        File::Data("b2".to_string(), 15),
+                    ],
+                ),
+                File::Data("c".to_string(), 8),
+            ],
+        );
+
+        assert_eq!(
+            du_sort(&rootfile),
+            vec![
+                ("a1", 1),
+                ("a2", 3),
+                ("b1", 3),
+                ("a", 4),
+                ("c", 8),
+                ("b2", 15),
+                ("b", 18),
+                ("root", 1 + 3 + 3 + 15 + 8)
+            ]
+        );
+
+        let rootfile = File::Directory(
+            "root".to_string(),
+            vec![
+                File::Directory(
+                    "b".to_string(),
+                    vec![
+                        File::Data("b1".to_string(), 3),
+                        File::Data("b2".to_string(), 15),
+                    ],
+                ),
+                File::Data("c".to_string(), 8),
+                File::Directory(
+                    "a".to_string(),
+                    vec![
+                        File::Data("a1".to_string(), 1),
+                        File::Data("a2".to_string(), 3),
+                    ],
+                ),
+            ],
+        );
+
+        assert_eq!(
+            du_sort(&rootfile),
+            vec![
+                ("a1", 1),
+                ("a2", 3),
+                ("b1", 3),
+                ("a", 4),
+                ("c", 8),
+                ("b2", 15),
+                ("b", 18),
+                ("root", 1 + 3 + 3 + 15 + 8)
+            ]
+        );
+
+        let rootfile = File::Directory(
+            "root".to_string(),
+            vec![
+                File::Directory(
+                    "a".to_string(),
+                    vec![
+                        File::Data("a1".to_string(), 1),
+                        File::Data("a2".to_string(), 3),
+                        File::Directory(
+                            "a3".to_string(),
+                            vec![
+                                File::Data("a31".to_string(), 1),
+                                File::Data("a32".to_string(), 3),
+                                File::Data("a33".to_string(), 6),
+                            ],
+                        ),
+                    ],
+                ),
+                File::Directory(
+                    "b".to_string(),
+                    vec![
+                        File::Data("b1".to_string(), 3),
+                        File::Data("b2".to_string(), 15),
+                    ],
+                ),
+                File::Data("c".to_string(), 16),
+            ],
+        );
+
+        assert_eq!(
+            du_sort(&rootfile),
+            vec![
+                ("a1", 1),
+                ("a31", 1),
+                ("a2", 3),
+                ("a32", 3),
+                ("b1", 3),
+                ("a33", 6),
+                ("a3", 10),
+                ("a", 14),
+                ("b2", 15),
+                ("c", 16),
+                ("b", 18),
+                ("root", 48)
+            ]
+        );
+    }
+
+    #[test]
+    fn test_remove_even() {
+        let mut vec = vec![1, 2, 3, 4, 5];
+        remove_even(&mut vec);
+        assert_eq!(*vec, vec![1, 3, 5]);
+
+        let mut vec = vec![11, 1000, 12, 101, 105, 104, 200];
+        remove_even(&mut vec);
+        assert_eq!(*vec, vec![11, 101, 105]);
+    }
+
+    #[test]
+    fn test_remove_duplicate() {
+        let mut vec = vec![1, 2, 1, 1, 3, 7, 5, 7];
+        remove_duplicate(&mut vec);
+
+        let set1: HashSet<i64> = HashSet::from_iter(vec);
+        let set2: HashSet<i64> = HashSet::from_iter(vec![1, 2, 3, 7, 5]);
+        assert_eq!(set1, set2);
+    }
+
+    #[test]
+    fn test_natural_join() {
+        let row1: Vec<String> = vec!["20230001", "Jack"]
+            .iter()
+            .map(|s| s.to_string())
+            .collect();
+        let row2: Vec<String> = vec!["20231234", "Mike"]
+            .iter()
+            .map(|s| s.to_string())
+            .collect();
+        let table1 = vec![row1, row2];
+        let row1: Vec<String> = vec!["20230001", "CS"]
+            .iter()
+            .map(|s| s.to_string())
+            .collect();
+        let row2: Vec<String> = vec!["20230001", "EE"]
+            .iter()
+            .map(|s| s.to_string())
+            .collect();
+        let row3: Vec<String> = vec!["20231234", "ME"]
+            .iter()
+            .map(|s| s.to_string())
+            .collect();
+        let table2 = vec![row1, row2, row3];
+        let row1: Vec<String> = vec!["20230001", "Jack", "CS"]
+            .iter()
+            .map(|s| s.to_string())
+            .collect();
+        let row2: Vec<String> = vec!["20230001", "Jack", "EE"]
+            .iter()
+            .map(|s| s.to_string())
+            .collect();
+        let row3: Vec<String> = vec!["20231234", "Mike", "ME"]
+            .iter()
+            .map(|s| s.to_string())
+            .collect();
+        let table3 = vec![row1, row2, row3];
+
+        assert_eq!(
+            HashSet::<Vec<String>>::from_iter(natural_join(table1, table2)),
+            HashSet::<Vec<String>>::from_iter(table3)
+        );
+
+        let row1: Vec<String> = vec!["20230001", "Alice"]
+            .iter()
+            .map(|s| s.to_string())
+            .collect();
+        let row2: Vec<String> = vec!["20230002", "Bob"]
+            .iter()
+            .map(|s| s.to_string())
+            .collect();
+        let row3: Vec<String> = vec!["20230003", "Charlie"]
+            .iter()
+            .map(|s| s.to_string())
+            .collect();
+        let row4: Vec<String> = vec!["20230004", "David"]
+            .iter()
+            .map(|s| s.to_string())
+            .collect();
+        let table1 = vec![row1, row2, row3, row4];
+        let row1: Vec<String> = vec!["20230001", "Apple"]
+            .iter()
+            .map(|s| s.to_string())
+            .collect();
+        let row2: Vec<String> = vec!["20230001", "Avocado"]
+            .iter()
+            .map(|s| s.to_string())
+            .collect();
+        let row3: Vec<String> = vec!["20230002", "Banana"]
+            .iter()
+            .map(|s| s.to_string())
+            .collect();
+        let row4: Vec<String> = vec!["20230002", "Berries"]
+            .iter()
+            .map(|s| s.to_string())
+            .collect();
+        let row5: Vec<String> = vec!["20230004", "Durian"]
+            .iter()
+            .map(|s| s.to_string())
+            .collect();
+        let table2 = vec![row1, row2, row3, row4, row5];
+        let row1: Vec<String> = vec!["20230001", "Alice", "Apple"]
+            .iter()
+            .map(|s| s.to_string())
+            .collect();
+        let row2: Vec<String> = vec!["20230001", "Alice", "Avocado"]
+            .iter()
+            .map(|s| s.to_string())
+            .collect();
+        let row3: Vec<String> = vec!["20230002", "Bob", "Banana"]
+            .iter()
+            .map(|s| s.to_string())
+            .collect();
+        let row4: Vec<String> = vec!["20230002", "Bob", "Berries"]
+            .iter()
+            .map(|s| s.to_string())
+            .collect();
+        let row5: Vec<String> = vec!["20230004", "David", "Durian"]
+            .iter()
+            .map(|s| s.to_string())
+            .collect();
+        let table3 = vec![row1, row2, row3, row4, row5];
+
+        assert_eq!(
+            HashSet::<Vec<String>>::from_iter(natural_join(table1, table2)),
+            HashSet::<Vec<String>>::from_iter(table3)
+        );
+    }
+
+    #[test]
+    fn test_pythagorean() {
+        let pythagoreans = [
+            (3, 4, 5),
+            (5, 12, 13),
+            (8, 15, 17),
+            (7, 24, 25),
+            (20, 21, 29),
+            (12, 35, 37),
+            (9, 40, 41),
+            (28, 45, 53),
+            (11, 60, 61),
+            (16, 63, 65),
+            (33, 56, 65),
+            (48, 55, 73),
+            (13, 84, 85),
+            (36, 77, 85),
+            (39, 80, 89),
+            (65, 72, 97),
+            (20, 99, 101),
+            (60, 91, 109),
+            (15, 112, 113),
+            (44, 117, 125),
+            (88, 105, 137),
+            (17, 144, 145),
+            (24, 143, 145),
+            (51, 140, 149),
+            (85, 132, 157),
+            (119, 120, 169),
+            (52, 165, 173),
+            (19, 180, 181),
+            (57, 176, 185),
+            (104, 153, 185),
+            (95, 168, 193),
+            (28, 195, 197),
+            (84, 187, 205),
+            (133, 156, 205),
+            (21, 220, 221),
+            (140, 171, 221),
+            (60, 221, 229),
+            (105, 208, 233),
+            (120, 209, 241),
+            (32, 255, 257),
+            (23, 264, 265),
+            (96, 247, 265),
+            (69, 260, 269),
+            (115, 252, 277),
+            (160, 231, 281),
+            (161, 240, 289),
+            (68, 285, 293),
+        ];
+
+        for (i, t) in pythagorean().enumerate().take(1000) {
+            if i < pythagoreans.len() {
+                assert_eq!(pythagoreans[i], t)
+            }
+            let (a, b, c) = t;
+            assert_eq!(a * a + b * b, c * c);
+        }
+    }
+}
--- a/src/assignments/assignment10_grade.rs
+++ b/src/assignments/assignment10_grade.rs
@@ -1,158 +0,0 @@
-#[cfg(test)]
-mod test {
-    use super::super::assignment10::*;
-
-    #[test]
-    fn test_inversion() {
-        assert_eq!(inversion(vec![3, 5, 4]), vec![(1, 2)]);
-        assert_eq!(inversion(vec!["c", "a", "b", "d"]), vec![(0, 1), (0, 2)]);
-        assert_eq!(
-            inversion(vec![2, 5, 4, 6, 3, 1]),
-            vec![
-                (0, 5),
-                (1, 2),
-                (1, 4),
-                (1, 5),
-                (2, 4),
-                (2, 5),
-                (3, 4),
-                (3, 5),
-                (4, 5)
-            ]
-        );
-    }
-
-    #[test]
-    fn test_traverse_preorder() {
-        let root = Node::NonLeaf((
-            1,
-            vec![
-                Node::NonLeaf((2, vec![Node::Leaf(5), Node::Leaf(6)])),
-                Node::Leaf(3),
-                Node::NonLeaf((4, vec![Node::Leaf(7), Node::Leaf(8), Node::Leaf(9)])),
-            ],
-        ));
-
-        assert_eq!(traverse_preorder(root), vec![1, 2, 5, 6, 3, 4, 7, 8, 9]);
-    }
-
-    #[test]
-    fn test_du_sort() {
-        let rootfile = File::Directory(
-            "root".to_string(),
-            vec![
-                File::Directory(
-                    "a".to_string(),
-                    vec![
-                        File::Data("a1".to_string(), 1),
-                        File::Data("a2".to_string(), 3),
-                    ],
-                ),
-                File::Directory(
-                    "b".to_string(),
-                    vec![
-                        File::Data("b1".to_string(), 3),
-                        File::Data("b2".to_string(), 15),
-                    ],
-                ),
-                File::Data("c".to_string(), 8),
-            ],
-        );
-
-        assert_eq!(
-            du_sort(&rootfile),
-            vec![
-                ("a1", 1),
-                ("a2", 3),
-                ("b1", 3),
-                ("a", 4),
-                ("c", 8),
-                ("b2", 15),
-                ("b", 18),
-                ("root", 1 + 3 + 3 + 15 + 8)
-            ]
-        );
-
-        let rootfile = File::Directory(
-            "root".to_string(),
-            vec![
-                File::Directory(
-                    "b".to_string(),
-                    vec![
-                        File::Data("b1".to_string(), 3),
-                        File::Data("b2".to_string(), 15),
-                    ],
-                ),
-                File::Data("c".to_string(), 8),
-                File::Directory(
-                    "a".to_string(),
-                    vec![
-                        File::Data("a1".to_string(), 1),
-                        File::Data("a2".to_string(), 3),
-                    ],
-                ),
-            ],
-        );
-
-        assert_eq!(
-            du_sort(&rootfile),
-            vec![
-                ("a1", 1),
-                ("a2", 3),
-                ("b1", 3),
-                ("a", 4),
-                ("c", 8),
-                ("b2", 15),
-                ("b", 18),
-                ("root", 1 + 3 + 3 + 15 + 8)
-            ]
-        );
-
-        let rootfile = File::Directory(
-            "root".to_string(),
-            vec![
-                File::Directory(
-                    "a".to_string(),
-                    vec![
-                        File::Data("a1".to_string(), 1),
-                        File::Data("a2".to_string(), 3),
-                        File::Directory(
-                            "a3".to_string(),
-                            vec![
-                                File::Data("a31".to_string(), 1),
-                                File::Data("a32".to_string(), 3),
-                                File::Data("a33".to_string(), 6),
-                            ],
-                        ),
-                    ],
-                ),
-                File::Directory(
-                    "b".to_string(),
-                    vec![
-                        File::Data("b1".to_string(), 3),
-                        File::Data("b2".to_string(), 15),
-                    ],
-                ),
-                File::Data("c".to_string(), 16),
-            ],
-        );
-
-        assert_eq!(
-            du_sort(&rootfile),
-            vec![
-                ("a1", 1),
-                ("a31", 1),
-                ("a2", 3),
-                ("a32", 3),
-                ("b1", 3),
-                ("a33", 6),
-                ("a3", 10),
-                ("a", 14),
-                ("b2", 15),
-                ("c", 16),
-                ("b", 18),
-                ("root", 48)
-            ]
-        );
-    }
-}
--- a/src/assignments/mod.rs
+++ b/src/assignments/mod.rs
@@ -15,15 +15,11 @@ mod assignment03_grade;
 pub mod assignment04;
 mod assignment04_grade;
 pub mod assignment06;
-mod assignment06_grade;
 pub mod assignment07;
-mod assignment07_grade;
 pub mod assignment08;
 mod assignment08_grade;
 pub mod assignment09;
-mod assignment09_grade;
 pub mod assignment10;
-mod assignment10_grade;
 pub mod assignment11;
 pub mod assignment12;
 pub mod assignment13;