class Solution {

int maximalSquare(vector<vector<char>>& matrix) {

int m = matrix.size();

if (!m) return 0;

int n = matrix[0].size();

vector<vector<int>> dp(m + 1, vector<int>(n + 1, 0));

int len = 0;

for (int i = 0; i < m; i++) {

for (int j = 0; j < n; j++) {

if (matrix[i][j] == '0') continue;

dp[i + 1][j + 1] = min(min(dp[i][j], dp[i + 1][j]), dp[i][j + 1]) + 1;

len = max(len , dp[i + 1][j + 1]);

}

}

return len * len;

}

};