Other
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.
来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/set-matrix-zeroes
很容易想到需要额外的空间$O(mn)$或者$O(m+n)$，如果希望不需要额外的空间，可以考虑用第一行和第一列作为标记，而第一行和第一列的标记则用两个常数标记即可。
class Solution {
public:
void setZeroes(vector<vector<int>>& matrix) {
int r = 1, c = 1;
for (int i = 0; i < matrix.size(); ++i) {
if (matrix[i][0] == 0) c = 0;
}
for (int j = 0; j < matrix[0].size(); ++j) {
if (matrix[0][j] == 0) r = 0;
}
for (int i = 1; i < matrix.size(); ++i) {
for (int j = 1; j < matrix[0].size(); ++j) {
if (matrix[i][j] == 0) {
matrix[0][j] = 0;
matrix[i][0] = 0;
}
}
}
for (int i = 1; i < matrix.size(); ++i) {
if (matrix[i][0] == 0) {
for (int j = 0; j < matrix[0].size(); ++j) matrix[i][j] = 0;
}
}
for (int j = 1; j < matrix[0].size(); ++j) {
if (matrix[0][j] == 0) {
for (int i = 0; i < matrix.size(); ++i) matrix[i][j] = 0;
}
}
if (c == 0) {
for (int i = 0; i < matrix.size(); ++i) matrix[i][0] = 0;
}
if (r == 0) {
for (int j = 0; j < matrix[0].size(); ++j) matrix[0][j] = 0;
}
}
};