Set Matrix Zeroes In Place in DSA Python - Build from Scratch

Set Matrix Zeroes In Place

📖 Scenario: You are working with a grid of numbers representing a seating chart in a theater. Some seats are broken and marked with zero. You want to mark all seats in the same row and column as broken if any seat in that row or column is broken.

🎯 Goal: Modify the given matrix in place so that if a seat is broken (0), all seats in that seat's row and column become broken (0).

📋 What You'll Learn

Create a 2D list called matrix with the exact values [[1,1,1],[1,0,1],[1,1,1]]

Create two variables called rows and cols to store the number of rows and columns in matrix

Use the first row and first column of matrix as markers to track which rows and columns should be zeroed

Modify matrix in place without using extra space for another matrix

Print the final matrix after modification

💡 Why This Matters

🌍 Real World

This technique is useful in image processing, seating arrangements, and spreadsheet software where marking entire rows and columns based on conditions is needed.

💼 Career

Understanding in-place matrix modification is important for optimizing memory usage in software engineering roles, especially in data processing and algorithm design.

1

Create the initial matrix

Create a 2D list called matrix with these exact values: [[1,1,1],[1,0,1],[1,1,1]]

DSA Python

# Create the matrix variable with the given values
# Your code here

Hint

Use square brackets to create a list of lists exactly as shown.

2

Set up row and column counts

Create two variables called rows and cols to store the number of rows and columns in matrix using len(matrix) and len(matrix[0]) respectively

DSA Python

matrix = [[1,1,1],[1,0,1],[1,1,1]]
# Create rows and cols variables to store matrix dimensions
# Your code here

Hint

Use len() to find the number of rows and columns.

3

Mark rows and columns to be zeroed

Use a for loop with variables r and c to iterate over all cells in matrix. If matrix[r][c] is 0, set matrix[r][0] and matrix[0][c] to 0 to mark the row and column

DSA Python

matrix = [[1,1,1],[1,0,1],[1,1,1]]
rows = len(matrix)
cols = len(matrix[0])
# Use nested for loops to mark rows and columns with zero
# Your code here

Hint

Check each cell and mark the first cell of its row and column if zero.

4

Set zeroes based on markers and print

Use nested for loops with variables r and c starting from 1 to rows and cols. If matrix[r][0] or matrix[0][c] is 0, set matrix[r][c] to 0. Then print the final matrix

DSA Python

matrix = [[1,1,1],[1,0,1],[1,1,1]]
rows = len(matrix)
cols = len(matrix[0])
for r in range(rows):
    for c in range(cols):
        if matrix[r][c] == 0:
            matrix[r][0] = 0
            matrix[0][c] = 0
# Use nested loops from 1 to rows and cols to set zeroes based on markers
# Then print the matrix
# Your code here

Hint

Start loops from 1 to avoid overwriting markers too early. Then print the matrix.