Set Matrix Zeroes In Place in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to mark the first row and column if a zero is found.

DSA Python

for i in range(len(matrix)):
    for j in range(len(matrix[0])):
        if matrix[i][j] == [1]:
            matrix[i][0] = 0
            matrix[0][j] = 0

Drag options to blanks, or click blank then click option'

A0

B-1

C1

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for 1 instead of 0.

Using None which is not a matrix element.

Using negative numbers which are not relevant here.

We check if the current element is zero to mark its row and column for zeroing later.

2fill in blank

medium

Complete the code to zero out cells based on the first row and column markers.

DSA Python

for i in range(1, len(matrix)):
    for j in range(1, len(matrix[0])):
        if matrix[i][0] == [1] or matrix[0][j] == 0:
            matrix[i][j] = 0

Drag options to blanks, or click blank then click option'

A1

B-1

C0

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for 1 instead of 0.

Using None or negative values incorrectly.

If either the row or column is marked zero, set the cell to zero.

3fill in blank

hard

Fix the error in the code that resets the first row to zero if needed.

DSA Python

if first_row_has_zero:
    for j in range(len(matrix[0])):
        matrix[0][j] = [1]

Drag options to blanks, or click blank then click option'

A0

B1

C-1

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Setting to 1 or None instead of zero.

Forgetting to reset the first row.

We set all elements in the first row to zero if the first row originally had any zero.

4fill in blank

hard

Fill both blanks to reset the first column to zero if needed.

DSA Python

if first_col_has_zero:
    for i in range([1]):
        matrix[i][[2]] = 0

Drag options to blanks, or click blank then click option'

Alen(matrix)

Blen(matrix[0])

C0

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using column length instead of row length for loop.

Using wrong column index.

We loop over all rows (len(matrix)) and set the first column (index 0) to zero.

5fill in blank

hard

Fill all three blanks to check if the first row and column have zeros initially.

DSA Python

first_row_has_zero = any(matrix[0][j] == [1] for j in range([2]))
first_col_has_zero = any(matrix[i][[3]] == 0 for i in range(len(matrix)))

Drag options to blanks, or click blank then click option'

A0

Blen(matrix[0])

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong indices for row or column.

Checking for 1 instead of 0.

We check if any element in the first row or first column is zero to mark flags.

Practice

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

easy

A. Find the sum of all elements in the matrix.

B. Modify the matrix so that if an element is 0, its entire row and column become 0.

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

D. Transpose the matrix without changing its elements.

Solution

1. Step 1: Understand the problem requirement

   The problem asks to change the matrix so that if any element is zero, all elements in that element's row and column become zero.

2. Step 2: Identify the correct description

   Modify the matrix so that if an element is 0, its entire row and column become 0. exactly describes this transformation, while others describe unrelated operations.

3. Final Answer:

   Modify the matrix so that if an element is 0, its entire row and column become 0. -> Option B

4. Quick Check:

   Set matrix zeroes means zero rows and columns [OK]

Hint: Remember zero means zero entire row and column [OK]

Common Mistakes:

• Confusing with matrix transpose
• Thinking only the zero element changes
• Trying to sum or sort instead

2. Which of the following Python code snippets correctly initializes a 3x3 matrix with all zeros?

easy

A. matrix = [[0]*3]*3

B. matrix = [0,0,0]*3

C. matrix = [0]*3 for _ in range(3)

D. matrix = [[0 for _ in range(3)] for _ in range(3)]

Solution

1. Step 1: Analyze each initialization method

   matrix = [[0]*3]*3 creates shallow copies of the same row, causing changes in one row to affect others. matrix = [[0 for _ in range(3)] for _ in range(3)] creates independent rows correctly. matrix = [0]*3 for _ in range(3) is invalid syntax. matrix = [0,0,0]*3 creates a flat list, not a matrix.

2. Step 2: Choose the correct matrix initialization

   Only matrix = [[0 for _ in range(3)] for _ in range(3)] correctly creates a 3x3 matrix with independent rows filled with zeros.

3. Final Answer:

   matrix = [[0 for _ in range(3)] for _ in range(3)] -> Option D

4. Quick Check:

   Use nested list comprehension for independent rows [OK]

Hint: Use nested list comprehension for 2D matrix [OK]

Common Mistakes:

• Using [[0]*3]*3 causes shared references
• Incorrect syntax in option C
• Flat list instead of 2D matrix

3. What will be the matrix after applying the Set Matrix Zeroes In Place logic on this matrix?

[[1, 2, 3],
 [4, 0, 6],
 [7, 8, 9]]

medium

A. [[1, 0, 3], [0, 0, 0], [7, 0, 9]]

B. [[1, 2, 3], [4, 0, 6], [7, 8, 9]]

C. [[1, 2, 3], [0, 0, 0], [7, 8, 9]]

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

Solution

1. Step 1: Identify zero positions

   The zero is at position (1,1) (second row, second column).

2. Step 2: Set entire row 1 and column 1 to zero

   Row 1 becomes [0,0,0]. Column 1 elements at rows 0 and 2 become zero, changing matrix to [[1,0,3],[0,0,0],[7,0,9]].

3. Final Answer:

   [[1, 0, 3], [0, 0, 0], [7, 0, 9]] -> Option A

4. Quick Check:

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

Hint: Zero row and column for each zero element [OK]

Common Mistakes:

• Not zeroing the entire column
• Changing elements not in zero row/column
• Confusing row and column indices

4. Given this code snippet to set matrix zeroes in place, what is the main bug?

def setZeroes(matrix):
    rows = len(matrix)
    cols = len(matrix[0])
    zero_rows = set()
    zero_cols = set()
    for i in range(rows):
        for j in range(cols):
            if matrix[i][j] == 0:
                zero_rows.add(i)
                zero_cols.add(j)
    for i in zero_rows:
        for j in range(cols):
            matrix[i][j] = 0
    for j in zero_cols:
        for i in range(rows):
            matrix[i][j] = 0

medium

A. It misses zeroing the diagonal elements.

B. It modifies the matrix before identifying all zeroes.

C. It uses extra space, not in-place modification.

D. It does not handle empty matrices.

Solution

1. Step 1: Analyze space usage

   The code uses sets zero_rows and zero_cols to store indices, which uses extra space proportional to matrix size.

2. Step 2: Understand in-place requirement

   The problem requires modifying the matrix without extra space (in-place). Using sets violates this.

3. Final Answer:

   It uses extra space, not in-place modification. -> Option C

4. Quick Check:

   Extra sets mean not in-place [OK]

Hint: In-place means no extra sets or arrays [OK]

Common Mistakes:

• Ignoring extra space used by sets
• Thinking diagonal needs special handling
• Assuming empty matrix causes error here

5. How can you modify the matrix [[1,2,3],[4,0,6],[7,8,9]] in place to set zeroes without using extra space for rows and columns? Which approach is correct?

hard

A. Use first row and first column as markers to track zero rows and columns, then update matrix accordingly.

B. Create two separate lists to store zero rows and columns, then update matrix.

C. Copy the matrix, modify the copy, then replace original matrix.

D. Only zero the rows where zero is found, ignore columns.

Solution

1. Step 1: Use first row and column as markers

   Mark zeros in first row and column to remember which rows and columns to zero later, avoiding extra space.

2. Step 2: Update matrix based on markers

   After marking, iterate matrix to set zeros in rows and columns indicated by markers, then handle first row and column separately.

3. Final Answer:

   Use first row and first column as markers to track zero rows and columns, then update matrix accordingly. -> Option A

4. Quick Check:

   First row/column markers enable in-place zeroing [OK]

Hint: Use matrix edges as markers to avoid extra space [OK]

Common Mistakes:

• Using extra lists violates in-place rule
• Copying matrix wastes space
• Ignoring zero columns leads to wrong result