LeetCode -- Set Matrix Zeroes

public class Solution {
    public void setZeroes(int[][] matrix) {
        ArrayList<Integer> colll = new ArrayList<Integer>();
        if(matrix == null)
            return;
        
        int row = matrix.length, col = matrix[0].length;
        boolean flag = false;
        for(int i=0; i<row; i++) {
            flag = false;
            for(int j=0; j<col; j++) {
                if(matrix[i][j] == 0) {
                    flag = true;
                    if(!colll.contains(j))
                        colll.add(j);
                }
            }
            if(flag == true) {
                for(int j=0; j<col; j++)
                matrix[i][j] = 0;
            }
        }
        
        for(int j=0; j<colll.size(); j++) {
            int temp = colll.get(j);
            for(int i=0; i<row; i++)
                matrix[i][temp] = 0;
        }
    }
}