[Medium]Maximal Square

问题：
Given a 2D binary matrix filled with 0’s and 1’s, find the largest square containing only 1’s and return its area.

For example, given the following matrix:

1 0 1 0 0
1 0 1 1 1
1 1 1 1 1
1 0 0 1 0
Return 4.
解法：

源码：

class Solution {public:    int maximalSquare(vector<vector<char>>& matrix) {        int n = matrix.size();        if (n == 0) return 0;        int m = matrix[0].size();        int f[n][m];        memset(f, 0, sizeof(f));        int ans = 0;        for (int i = 0; i < n; ++i) {            for (int j = 0; j < m; ++j) {                if (i == 0 || j == 0) {                    f[i][j] = matrix[i][j] - '0';                } else {                    f[i][j] = matrix[i][j] - '0';                    if (f[i][j]) f[i][j] = min(min(f[i-1][j], f[i][j-1]), f[i-1][j-1]) + 1;                }                ans = max(ans, f[i][j]);            }        }        return ans * ans;    }};