5pts，试的数据都对但是只有#1不是0

rt,没想做优化，就单打暴力，但是交上去只有第一个点输出不是0，剩下都是0，自己在本地测了其他帖的数据也没问题，求调

#include <iostream>
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <fstream>
using namespace std;
char a[1000][1000],n,m,ans;

bool count(int _a,int _b,int _c,int _d){
    int x=0,y=0;
    for (int i=_a;i<=_c;i++){
        for (int j=_b;j<=_d;j++){
            if (a[i][j] == '1') x+=1;
            else y+=1;
        }
    }
    //cout<<x<<" "<<y<<endl;
    if (x==y) return true;
    return false;
}
int main(){
    scanf ("%d %d", &n, &m);
    for (int i=1;i<=n;i++){
        for (int j=1;j<=m;j++) cin>>a[i][j];
    }
    for (int i=1;i<=n;i++){
        for (int j=1;j<=m;j++){
            for (int k=i;k<=n;k++){
                for (int _i = j;_i<=m;_i++){
                    //cout<<i<<" "<<j<<" "<<k<<" "<<_i<<endl;
                    if (count(i,j,k,_i)){
                        ans = (k-i+1)*(_i-j+1)>ans?(k-i+1)*(_i-j+1):ans;
                    }
                }
            }
        }
    }
    printf ("%d\n",ans);
    return 0;
}