Set Matrix Zeros

class Solution {
    public void setMatrixZeroes(int[][] mat) {
        int n = mat.length;
        int m = mat[0].length;

        int col0 = 1;
        // step 1: Traverse the matrix and
        // mark 1st row & col accordingly:
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                if (mat[i][j] == 0) {
                    // mark i-th row:
                    mat[i][0] = 0;

                    // mark j-th column:
                    if (j != 0)
                        mat[0][j] = 0;
                    else
                        col0 = 0;
                }
            }
        }

        // Step 2: Mark with 0 from (1,1) to (n-1, m-1):
        for (int i = 1; i < n; i++) {
            for (int j = 1; j < m; j++) {
                if (mat[i][j] != 0) {
                    // check for col & row:
                    if (mat[i][0] == 0 || mat[0][j] == 0)
                        mat[i][j] = 0;
                }
            }
        }

        // step 3: Finally mark the 1st col & then 1st row:
        if (mat[0][0] == 0) {
            for (int j = 0; j < m; j++)
                mat[0][j] = 0;
        }
        if (col0 == 0) {
            for (int i = 0; i < n; i++)
                mat[i][0] = 0;
        }
    }
}