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class Solution {
public:
    int maximalSquare(vector<vector<char>>& mat) {
        int rows = mat.size(), cols = mat[0].size();
        int len = 0, dp[rows][cols];

        for(int i=0; i<rows; i++){
            for(int j=0; j<cols; j++){
                dp[i][j] = (mat[i][j] == '1') ? 1 : 0;
                if(dp[i][j] && i && j){
                    int sz = min({dp[i-1][j], dp[i][j-1], dp[i-1][j-1]});
                    dp[i][j] = sz+1;
                }
                len = max(len, dp[i][j]);
            }
        }

        return len*len;
    }
};