LeetCode-in-All

73. Set Matrix Zeroes

Medium

Given an m x n integer matrix matrix, if an element is 0, set its entire row and column to 0’s.

You must do it in place.

Example 1:

Input: matrix = [[1,1,1],[1,0,1],[1,1,1]]

Output: [[1,0,1],[0,0,0],[1,0,1]]

Example 2:

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

Output: [[0,0,0,0],[0,4,5,0],[0,3,1,0]]

Constraints:

• m == matrix.length
• n == matrix[0].length
• 1 <= m, n <= 200
• -231 <= matrix[i][j] <= 231 - 1

Follow up:

• A straightforward solution using O(mn) space is probably a bad idea.
• A simple improvement uses O(m + n) space, but still not the best solution.
• Could you devise a constant space solution?

Solution

#include <stdio.h>
#include <stdlib.h>

void setZeroRow(int **matrix, int cols, int row) {
    for (int j = 0; j < cols; j++) {
        matrix[row][j] = 0;
    }
}

void setZeroCol(int **matrix, int rows, int col) {
    for (int i = 0; i < rows; i++) {
        matrix[i][col] = 0;
    }
}

void setZeroes(int** matrix, int matrixSize, int* matrixColSize) {
    int setFirstRow = 0, setFirstCol = 0;

    // Step 1: Determine which rows and columns to zero out
    for (int i = 0; i < matrixSize; i++) {
        for (int j = 0; j < *matrixColSize; j++) {
            if (matrix[i][j] == 0) {
                matrix[i][0] = 0;  // Mark the first column
                matrix[0][j] = 0;  // Mark the first row

                if (i == 0) setFirstRow = 1;  // Indicate first row needs to be zeroed
                if (j == 0) setFirstCol = 1;  // Indicate first column needs to be zeroed
            }
        }
    }

    // Step 2: Zero out cells based on marks in the first row and column
    for (int i = matrixSize - 1; i > 0; i--) {
        if (matrix[i][0] == 0) {
            setZeroRow(matrix, *matrixColSize, i);
        }
    }

    for (int j = *matrixColSize - 1; j > 0; j--) {
        if (matrix[0][j] == 0) {
            setZeroCol(matrix, matrixSize, j);
        }
    }

    // Step 3: Zero out the first row and column if needed
    if (setFirstRow) {
        setZeroRow(matrix, *matrixColSize, 0);
    }
    if (setFirstCol) {
        setZeroCol(matrix, matrixSize, 0);
    }
}

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