Java版本

import java.util.*;
import java.io.*;
public class Main{
    public static void main(String[] args) throws Exception{
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] strs1 = br.readLine().split(" ");
        int rows = Integer.parseInt(strs1[0]);
        int cols = Integer.parseInt(strs1[1]);
        int[][] dp = new int[rows][cols];
        int[][] matrix = new int[rows][cols];
        for(int i = 0; i < rows; i++){
            String[] strs = br.readLine().split(" ");
            for(int j = 0; j < cols; j++){
                matrix[i][j] = Integer.parseInt(strs[j]);
            }
        }
        int maxSquareLength = 0;
        for(int i = 0; i < rows; i++){
            if(matrix[i][0] == 1) dp[i][0] = 1;
        }
        for(int i = 0; i < cols; i++){
            if(matrix[0][i] == 1) dp[0][i] = 1;
         }
        for(int  i =1; i < rows; i++){
            for(int j = 1; j < cols; j++){
                if(matrix[i][j] == 1){
                    dp[i][j] = Math.min(Math.min(dp[i-1][j-1],dp[i-1][j]),dp[i][j-1])+1;
                    if(dp[i][j] > maxSquareLength) maxSquareLength = dp[i][j];
                }
            }
        }
        System.out.println( maxSquareLength*maxSquareLength);
    }
}