[C++] 1051 - 숫자 정사각형

#include<iostream>
#include<algorithm>
 
using namespace std;
 
int board[55][55];
 
int main(void)
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
 
    char ch;
    int N, M;
    int ans, ANS;
 
    ans = ANS = 0;
    cin >> N >> M;
 
    for(int i =0; i < N; ++i)
    {
        for(int j = 0; j < M; ++j)
        {
            cin >> ch;
            board[i][j] = ch-'0';
        }
    }
 
    for(int i = 0; i < N; ++i)
    {
        for(int j = 0; j < M; ++j)
        {
            for(int k = 0; j+k < M && i+k < N; ++k)
            {
                if(board[i][j] == board[i+k][j] && board[i][j] == board[i][j+k] && board[i][j] == board[i+k][j+k])
                    ans = (k+1)*(k+1);
                if(ANS < ans)
                    ANS = ans;
            }
        }
    }
 
    cout << ANS << endl;
 
 
    return 0;
}