LeetCode 73. Set Matrix Zeroes

Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place.

// Only provides in-place method. The trick is to remember the 0s in the first row and first column.

 void setZeroes(vector<vector<int>>& matrix) {
    if(matrix.size() == 0) return;
    if(matrix[0].size() == 0) return;

    int rows = matrix.size();
    int cols = matrix[0].size();

    bool rowZero = false;
    bool colZero = false;
    
    for(int i = 0; i < cols; ++i) {
        if(matrix[0][i] == 0) {
            rowZero = true;
            break;
        }
    }

    for(int j = 0; j < rows; ++j) {
        if(matrix[j][0] == 0) {
            colZero = true;
            break;
        }
    }

    for(int i = 1; i < rows; ++i) {
        for(int j = 1; j < cols; ++j) {
            if(matrix[i][j] == 0) {
                matrix[i][0] = 0;
                matrix[0][j] = 0;  // remember to 0s to the first row and first column.
            }
        }
    }

    for(int i = 1; i < rows; ++i) {
        for(int j = 1; j < cols; ++j) {
            if(matrix[i][0] == 0 || matrix[0][j] == 0) {
                matrix[i][j] = 0;  // apply them back.
            }
        }
    }

    if(rowZero) {
        for(int i = 0; i < cols; ++i) {
            matrix[0][i] = 0;
        }
    }
    if(colZero) {
        for(int i = 0; i < rows; ++i) {
            matrix[i][0] = 0;
        }
    }
}