FYI. https://yunlinsong.blogspot.com/2019/11/b027.html

b027.cpp

#include <iostream>    
    
using namespace std;    
    
int main()    
{    
    int board[100][100] = {0};    
    int h, w;    
    
    cin >> h >> w;    
  
    // 因為題目可蓋城堡是用 0 表示，  
    // 所以將 0 變 1、1 變 0，來配合演算法  
    for(int i = 0; i < h; i++)    
    {    
        for(int j = 0; j < w; j++)    
        {    
            cin >> board[i][j];    
            board[i][j] = 1 - board[i][j];    
        }    
    }    
    
    int maxSqLen = 0;    
    
    for(int i = 1; i < h; i++)    
    {    
        for(int j = 1; j < w; j++)    
        {    
            if(board[i-1][j-1] >= 1 && board[i][j] == 1)    
            {    
                board[i][j] = min(board[i][j-1], min(board[i-1][j-1], board[i-1][j])) + 1;    
                maxSqLen = max(maxSqLen, board[i][j]);    
            }    
        }    
    }    
    
    int area = maxSqLen * maxSqLen;    
    cout << area << endl;    
    
    return 0;    
}