Set Matrix Zeroes In Place in DSA Rust - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output after setting zeroes in matrix

What is the state of the matrix after running the Set Matrix Zeroes In Place algorithm on the given input?

DSA Rust

let mut matrix = vec![
    vec![1, 1, 1],
    vec![1, 0, 1],
    vec![1, 1, 1],
];

// After calling set_zeroes(&mut matrix)
// What is the matrix now?

A [[1, 0, 1], [0, 0, 0], [1, 0, 1]]

B [[1, 0, 1], [1, 0, 1], [1, 0, 1]]

C [[0, 0, 0], [0, 0, 0], [0, 0, 0]]

D [[1, 1, 1], [1, 0, 1], [1, 1, 1]]

💡 Hint

Remember that if an element is zero, its entire row and column must be set to zero.

The zero at position (1,1) causes the entire row 1 and column 1 to be zeroed. So the matrix becomes [[1,0,1],[0,0,0],[1,0,1]].

❓ Predict Output

intermediate

Resulting matrix after zeroing rows and columns

Given the matrix below, what is the matrix after applying the Set Matrix Zeroes In Place algorithm?

DSA Rust

let mut matrix = vec![
    vec![0, 2, 3],
    vec![4, 5, 6],
    vec![7, 8, 0],
];

// After set_zeroes(&mut matrix), what is matrix?

A [[0, 0, 0], [0, 5, 0], [0, 0, 0]]

B [[0, 2, 3], [4, 5, 6], [7, 8, 0]]

C [[0, 0, 0], [0, 0, 0], [0, 0, 0]]

D [[0, 2, 0], [0, 5, 0], [0, 0, 0]]

💡 Hint

Zeros in first row and last column affect their rows and columns.

Zeros at (0,0) and (2,2) cause row 0, column 0, row 2, and column 2 to be zeroed. So matrix[0][1] and matrix[1][0], matrix[1][2], matrix[2][0..2] are zero.

🔧 Debug

advanced

Identify the error in this Set Matrix Zeroes implementation

What error will this Rust code cause when run on an empty matrix?

DSA Rust

fn set_zeroes(matrix: &mut Vec<Vec<i32>>) {
    let rows = matrix.len();
    let cols = matrix[0].len();
    let mut zero_rows = vec![false; rows];
    let mut zero_cols = vec![false; cols];

    for i in 0..rows {
        for j in 0..cols {
            if matrix[i][j] == 0 {
                zero_rows[i] = true;
                zero_cols[j] = true;
            }
        }
    }

    for i in 0..rows {
        for j in 0..cols {
            if zero_rows[i] || zero_cols[j] {
                matrix[i][j] = 0;
            }
        }
    }
}

// What error occurs if matrix is empty?

A TypeError because of mismatched types

B No error, works fine for empty matrix

C IndexOutOfBounds panic due to accessing matrix[0] when matrix is empty

D Stack overflow due to infinite recursion

💡 Hint

Check how matrix[0].len() behaves if matrix is empty.

If matrix is empty, matrix[0] access causes panic because there is no first row.

🧠 Conceptual

advanced

Space complexity of in-place Set Matrix Zeroes algorithm

What is the space complexity of the optimal in-place Set Matrix Zeroes algorithm that uses the first row and first column as markers?

A O(m * n) extra space

B O(m + n) extra space where m and n are matrix dimensions

C O(log(m + n)) extra space

D O(1) constant extra space

💡 Hint

The algorithm uses the matrix itself to store zero markers.

By using first row and column as markers, no extra arrays are needed, so space is constant.

🚀 Application

expert

After applying Set Matrix Zeroes, how many non-zero elements remain?

Given the matrix below, after applying the Set Matrix Zeroes In Place algorithm, how many elements remain non-zero?

DSA Rust

let mut matrix = vec![
    vec![1, 2, 3, 4],
    vec![5, 0, 7, 8],
    vec![9, 10, 11, 12],
    vec![0, 14, 15, 16],
];

// After set_zeroes(&mut matrix), count non-zero elements.

A 6

B 4

C 8

D 10

💡 Hint

Identify rows and columns with zeros and count remaining non-zero elements.

Zeros at (1,1) and (3,0) zero rows 1 and 3, columns 0 and 1. Remaining non-zero elements are at positions (0,2),(0,3),(2,2),(2,3). Total 4 non-zero elements.

Practice

1. What is the main goal of the Set Matrix Zeroes In Place problem?

easy

A. Sort each row of the matrix in ascending order.

B. Count the number of zero elements in the matrix.

C. Modify the matrix so that if an element is 0, its entire row and column become 0 without using extra space.

D. Replace all zero elements with ones.

Solution

1. Step 1: Understand the problem requirement

   The problem asks to set entire rows and columns to zero if any element in them is zero, modifying the matrix directly without extra space.

2. Step 2: Differentiate from other options

   Options A, B, and C do not match the problem's goal of modifying rows and columns based on zero elements.

3. Final Answer:

   Modify the matrix so that if an element is 0, its entire row and column become 0 without using extra space. -> Option C

4. Quick Check:

   Goal = Modify matrix rows and columns in place [OK]

Hint: Focus on zero elements affecting entire rows and columns [OK]

Common Mistakes:

• Thinking only to count zeros
• Trying to use extra memory
• Confusing with sorting or replacing zeros

2. Which Rust syntax correctly declares a mutable 2D vector named matrix with 3 rows and 3 columns initialized to 1?

easy

A. let mut matrix = vec![vec![1; 3]; 3];

B. let mut matrix = vec![1; 3][3];

C. let matrix = vec![vec![1; 3]; 3];

D. let matrix = vec![1; 3][3];

Solution

1. Step 1: Identify mutable declaration

   To modify the matrix later, it must be declared mutable using let mut.

2. Step 2: Correct 2D vector initialization

   The syntax vec![vec![1; 3]; 3] creates a 3x3 vector filled with 1s. Options B and D are invalid syntax. let matrix = vec![vec![1; 3]; 3]; lacks mut.

3. Final Answer:

   let mut matrix = vec![vec![1; 3]; 3]; -> Option A

4. Quick Check:

   Mutable 2D vector with correct syntax = let mut matrix = vec![vec![1; 3]; 3]; [OK]

Hint: Use let mut and nested vec! for 2D vectors [OK]

Common Mistakes:

• Forgetting mut keyword
• Using invalid vector syntax
• Confusing 1D and 2D vector initialization

3. Given the following Rust code snippet, what will be the printed matrix after calling set_zeroes(&mut matrix)?

fn set_zeroes(matrix: &mut Vec) {
    let rows = matrix.len();
    let cols = matrix[0].len();
    let mut row_zero = false;

    for i in 0..rows {
        if matrix[i][0] == 0 {
            row_zero = true;
        }
        for j in 1..cols {
            if matrix[i][j] == 0 {
                matrix[i][0] = 0;
                matrix[0][j] = 0;
            }
        }
    }

    for i in 1..rows {
        for j in 1..cols {
            if matrix[i][0] == 0 || matrix[0][j] == 0 {
                matrix[i][j] = 0;
            }
        }
    }

    if matrix[0][0] == 0 {
        for j in 0..cols {
            matrix[0][j] = 0;
        }
    }

    if row_zero {
        for i in 0..rows {
            matrix[i][0] = 0;
        }
    }
}

fn main() {
    let mut matrix = vec![
        vec![1, 1, 1],
        vec![1, 0, 1],
        vec![1, 1, 1],
    ];
    set_zeroes(&mut matrix);
    for row in matrix {
        println!("{:?}", row);
    }
}

medium

A. [[1, 0, 1], [0, 0, 0], [1, 0, 1]]

B. [[1, 1, 1], [1, 0, 1], [1, 1, 1]]

C. [[0, 0, 0], [0, 0, 0], [0, 0, 0]]

D. [[1, 1, 1], [0, 0, 0], [1, 1, 1]]

Solution

1. Step 1: Identify zero positions and mark rows and columns

   The zero is at position (1,1). The first loop marks row 1 and column 1 by setting matrix[1][0] and matrix[0][1] to zero.

2. Step 2: Set zeros based on marks

   The second loop sets elements to zero if their row or column is marked. This changes matrix[0][1], matrix[1][0..2], and matrix[2][1] to zero.

3. Final Answer:

   [[1, 0, 1], [0, 0, 0], [1, 0, 1]] -> Option A

4. Quick Check:

   Zero at (1,1) affects row 1 and column 1 [OK]

Hint: Mark first row and column to track zeros, then update matrix [OK]

Common Mistakes:

• Not marking first row and column correctly
• Overwriting zeros too early
• Ignoring the first column zero flag

4. The following Rust function attempts to set matrix zeroes in place but has a bug. What is the bug?

fn set_zeroes(matrix: &mut Vec) {
    let rows = matrix.len();
    let cols = matrix[0].len();

    for i in 0..rows {
        for j in 0..cols {
            if matrix[i][j] == 0 {
                for k in 0..rows {
                    matrix[k][j] = 0;
                }
                for l in 0..cols {
                    matrix[i][l] = 0;
                }
            }
        }
    }
}

medium

A. It does not check for empty matrix before accessing elements.

B. It modifies the matrix while iterating, causing incorrect zero propagation.

C. It uses incorrect loop ranges causing out-of-bounds errors.

D. It uses immutable references instead of mutable ones.

Solution

1. Step 1: Analyze matrix modification during iteration

   The function sets zeros immediately when it finds a zero, which changes the matrix during iteration.

2. Step 2: Understand effect of immediate modification

   This causes new zeros to be found in later iterations, incorrectly zeroing more rows and columns than intended.

3. Final Answer:

   It modifies the matrix while iterating, causing incorrect zero propagation. -> Option B

4. Quick Check:

   Immediate zeroing during iteration causes errors [OK]

Hint: Avoid changing matrix while scanning for zeros; mark first then update [OK]

Common Mistakes:

• Changing matrix elements inside nested loops
• Not using markers to delay zeroing
• Ignoring matrix size checks

5. You have a 4x4 matrix:

[
  [1, 2, 0, 4],
  [5, 6, 7, 8],
  [9, 0, 11, 12],
  [13, 14, 15, 16]
]

Using the in-place algorithm that uses the first row and column as markers, what will be the matrix after applying set_zeroes?

hard

A. [[0, 0, 0, 0], [5, 6, 0, 8], [0, 0, 0, 0], [13, 14, 0, 16]]

B. [[1, 2, 0, 4], [5, 6, 0, 8], [0, 0, 0, 0], [13, 14, 0, 16]]

C. [[0, 2, 0, 4], [5, 6, 0, 8], [0, 0, 0, 0], [13, 14, 0, 16]]

D. [[0, 0, 0, 0], [5, 0, 0, 8], [0, 0, 0, 0], [13, 0, 0, 16]]

Solution

1. Step 1: Mark rows and columns using first row and column

   Zeros at (0,2) and (2,1) mark row 0, row 2, column 2, and column 1 as zero.

2. Step 2: Update matrix based on markers

   Set all elements in rows 0 and 2, and columns 1 and 2 to zero. Also, since matrix[0][0] is zero (due to marking), first row is zeroed. First column is zeroed only where rows are marked since no original first column zero.

3. Final Answer:

   [[0, 0, 0, 0], [5, 0, 0, 8], [0, 0, 0, 0], [13, 0, 0, 16]] -> Option D

4. Quick Check:

   First row and column mark zeros correctly [OK]

Hint: Remember to zero first row and column if marked [OK]

Common Mistakes:

• Forgetting to zero first row or column
• Not marking all affected rows and columns
• Incorrectly zeroing unrelated cells