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.

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这题目关键是要求O(1)的空间。

可以使用第1行，第1列来保存数据信息。

class Solution {
public:
void setZeroes(vector<vector<int> > &matrix) {

bool firstrow = false;
bool firstcol = false;
for(int j = 0; j < col; ++j)
if(matrix[0][j] == 0){
firstrow = true;
break;
}
for(int i = 0; i < row; ++i)
if(matrix[i][0] == 0){
firstcol = true;
break;
}

for(int i = 1; i < row; ++i)
for(int j = 1; j < col; ++j){
if(matrix[i][j] == 0) {
matrix[i][0] = 0;
matrix[0][j] = 0;
}
}

for(int i = 1; i < row; ++i)
for(int j = 1; j < col; ++j)
if(matrix[i][0] == 0 || matrix[0][j] == 0)
matrix[i][j] = 0;

if(firstrow){
for(int j = 0; j < col; ++j)
matrix[0][j] = 0;
}
if(firstcol){
for(int i = 0; i < row; ++i)
matrix[i][0] = 0;
}
}
};