public class Solution {
    public int maximalSquare(char[][] matrix) {
        if(matrix.length == 0) return 0;

        int row = matrix.length;
        int col = matrix[0].length;
        int maxSum = 0;
        int[][] dp = new int[row + 1][col + 1];



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

                if(matrix[i-1][j-1] == '1'){
                    int x = Math.min(dp[i-1][j], dp[i][j-1]);
                    dp[i][j] = Math.min(x, dp[i-1][j-1]) + 1;
                    //System.out.println("cacat");
                }
                if(dp[i][j] > maxSum)
                    maxSum = dp[i][j];
            }
        }
        return maxSum * maxSum;
    }
}