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

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of the matrix after running the code?

Given the matrix below, what will be its state after applying the Set Matrix Zeroes In Place algorithm?

DSA Python

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

# After running the algorithm, print the matrix row-wise

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

B [[1, 0, 3], [0, 0, 0], [0, 0, 0]]

C [[1, 0, 3], [0, 0, 0], [7, 0, 9]]

D [[1, 0, 3], [4, 0, 6], [7, 0, 9]]

💡 Hint

Remember that if an element is zero, its entire row and column become zero.

The zero at position (1,1) causes the entire row 1 and column 1 to be zeroed. So, row 1 becomes all zeros, and column 1 elements in other rows become zero.

❓ Predict Output

intermediate

What is the output matrix after applying the algorithm?

Consider this matrix. What will it look like after applying the Set Matrix Zeroes In Place algorithm?

DSA Python

matrix = [
  [0, 1, 2, 0],
  [3, 4, 5, 2],
  [1, 3, 1, 5]
]

# Print the matrix row-wise after the algorithm

A [[0, 0, 0, 0], [0, 4, 5, 0], [0, 3, 1, 0]]

B [[0, 1, 2, 0], [3, 4, 5, 2], [1, 3, 1, 5]]

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

D [[0, 0, 0, 0], [3, 4, 5, 2], [1, 3, 1, 5]]

💡 Hint

Zeros in the first row cause their columns and rows to be zeroed.

The zeros at positions (0,0) and (0,3) cause row 0 and columns 0 and 3 to be zeroed. Rows 1 and 2 have zeros in columns 0 and 3 respectively.

🔧 Debug

advanced

What error does this code raise when run?

This code tries to set matrix zeroes in place. What error will it raise?

DSA Python

def set_zeroes(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

matrix = [[1,2,3],[4,0,6],[7,8,9]]
set_zeroes(matrix)
print(matrix[3])

A TypeError: 'int' object is not subscriptable

B IndexError: list index out of range

C No error, prints [7, 8, 9]

D AttributeError: 'set' object has no attribute 'append'

💡 Hint

Check the print statement accessing matrix[3].

The matrix has 3 rows indexed 0,1,2. Accessing matrix[3] is out of range, causing IndexError.

🧠 Conceptual

advanced

How many elements are set to zero after running the algorithm on this matrix?

Given the matrix below, how many elements will be zero after applying the Set Matrix Zeroes In Place algorithm?

DSA Python

matrix = [
  [1, 2, 0],
  [4, 5, 6],
  [0, 8, 9]
]

A 6

B 5

C 4

D 8

💡 Hint

Count zeros in rows and columns affected by zeros.

Zeros at (0,2) and (2,0) cause row 0, row 2, column 0, and column 2 to be zeroed. Counting all zeroed elements gives 8.

🚀 Application

expert

What is the final matrix after applying the algorithm in place?

Apply the Set Matrix Zeroes In Place algorithm on this matrix and provide the final matrix state.

DSA Python

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

# Print matrix row-wise after algorithm

A [[0, 0, 3, 4], [0, 0, 0, 0], [0, 0, 11, 12], [0, 0, 0, 0]]

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

C [[1, 0, 3, 4], [5, 0, 7, 8], [9, 0, 11, 12], [0, 0, 0, 0]]

D [[0, 2, 3, 4], [0, 0, 0, 0], [0, 10, 11, 12], [0, 0, 0, 0]]

💡 Hint

Zeros at (1,1) and (3,0) affect their rows and columns.

The zero at (1,1) zeroes row 1 and column 1. The zero at (3,0) zeroes row 3 and column 0. Combining these, the final matrix is as in option A.