二位前缀和

因为数据量很低 其实可以暴力枚举

#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,m;
    cin>>n>>m;
    int a[13][13]={};
    int x=0;
    
    for (int i=1;i<=n;i++){
    	for (int j=1;j<=m;j++){
    		cin>>x;
            a[i][j]=a[i-1][j]+a[i][j-1]-a[i-1][j-1]+x;
    	}
    }//求二维前缀和
    
    int mx=0;
    for (int x1=1;x1<=n;x1++){
    	for (int y1=1;y1<=m;y1++){
    		for (int x2=x1;x2<=n;x2++){
    			for (int y2=y1;y2<=m;y2++){//四重循环枚举左上角和右下角
    				if ((x2-x1+1)*(y2-y1+1)==a[x2][y2]-a[x2][y1-1]-a[x1-1][y2]+a[x1-1][y1-1]){
                    	mx=max((x2-x1+1)*(y2-y1+1),mx);
                    }
    			}
    		}
    	}
    }
    
	cout<<mx;
    return 0;
}