class Solution {
    public int maximalSquare(char[][] matrix) {
        int row = matrix.length, col = row>0 ? matrix[0].length : 0, max = 0;
        int [][] dp = new int[row+1][col+1];
        for(int i=1; i<=row; i++)
        {
            for(int j=1; j<=col; j++)
            {
                if(matrix[i-1][j-1]=='1')
                {
                    dp[i][j] = Math.min(Math.min(dp[i-1][j], dp[i][j-1]), dp[i-1][j-1])+1;
                    max = Math.max(max, dp[i][j]);
                }
            }
        }
        return max*max;
    }
}