51nod1158 全是1的最大子矩阵

#include<cstdio>
#include<cstring>
#include<cctype>
#include<algorithm>
using namespace std;
#define rep(i,s,t) for(int i=s;i<=t;i++)
#define dwn(i,s,t) for(int i=s;i>=t;i--)
int read(){
	int x=0;char c=getchar();
	while(!isdigit(c)) c=getchar();
	while(isdigit(c)) x=x*10+c-‘0‘,c=getchar();
	return x;
}
const int nmax=505;
int a[nmax][nmax];
void maxs(int &a,int b){
	if(a<b) a=b;
}
int main(){
	int m=read(),n=read();
	rep(i,1,n) rep(j,1,m) a[i][j]=read(),a[i][j]+=a[i-1][j];
	int ans=0,cnt;
	rep(i,1,n) rep(j,i,n) {
		cnt=0;
		rep(k,1,m){
		    if(a[j][k]-a[i-1][k]!=j-i+1) maxs(ans,cnt*(j-i+1)),cnt=0;
		    else cnt++;
	    }
	    maxs(ans,cnt*(j-i+1));
	}
	printf("%d\n",ans);
	return 0;
}