图片说明 

import java.util.*;


public class Solution {
    /**
     * 最大正方形
     * @param matrix char字符型二维数组 
     * @return int整型
     */
    public int solve (char[][] matrix) {
        // write code here
        int m = matrix.length;
        int n = matrix[0].length;
        int max = 0;
        int dp[][] = new int [m][n];
        for(int i = 0; i < m; i++){
            for(int j = 0; j < n; j++){
                dp[i][j] = matrix[i][j] - '0';
                if(dp[i][j] == 1) max = 1;
            }
        }
        for(int i = 1; i < m; i++){
            for(int j = 1; j < n; j++){
                if(dp[i][j] == 1){
                    dp[i][j] = Math.min(Math.min(dp[i-1][j-1],dp[i][j-1]),dp[i-1][j]) + 1;
                    max = Math.max(max,dp[i][j]);
                }
            }
        }
        return max*max;
    }
}