Set Matrix Zeroes

题目
Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place.
Follow up:
Did you use extra space?
A straight forward 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?

0 0 0 0
0 0 0 0
1 0 1 0

b = does first column have zero? = no
0 0 0 0
0 0 0 0
1 0 1 0

答案

O(mn) space

给定matrix A, 拷贝一个新的matrix B.
如果B[i][j] = 0, 则把A的第i行和第j列填0

O(m+n) space

if A[i][j] = 0, then list1.add(i), list2.add(j)
然后把list1里的行和list2里的列清0

O(1) (太长，以后缩减一下)

class Solution {
    public void setZeroes(int[][] matrix) {
        // Does first row, column have zeroes?
        int m = matrix.length, n = matrix[0].length;
        boolean first_row = false;
        boolean first_col = false;

        for(int i = 0; i < m; i++) {
            if(matrix[i][0] == 0) {
                first_col = true;
                break;
            }
        }

        for(int j = 0; j < n; j++) {
            if(matrix[0][j] == 0) {
                first_row = true;
                break;
            }
        }
        
        for(int i = 1; i < m; i++) {
            for(int j = 1; j < n; j++) {
                if(matrix[i][j] == 0) {
                    matrix[0][j] = 0;
                    matrix[i][0] = 0;
                }
            }
        }
        
        for(int i = 1; i < m; i++) {
            if(matrix[i][0] == 0) {
                // Set this row to 0
                for(int j = 1; j < n; j++) matrix[i][j] = 0;
            }
        }

        for(int j = 1; j < n; j++) {
            if(matrix[0][j] == 0) {
                // Set this col to 0
                for(int i = 1; i < m; i++) matrix[i][j] = 0;
            }
        }
        if(first_row)
            for(int j = 0; j < n; j++) matrix[0][j] = 0;
        if(first_col)
            for(int i = 0; i < m; i++) matrix[i][0] = 0;
    }
}