HDU 2830 Matrix Swapping II

#include <cstdio>
#include<iostream>
#include <cstring>
#include <algorithm>
using namespace std;
int a[1010],b[1010];
bool cmp(int t1,int t2)
{
return t1>t2;
}
int main()
{
int i,j,n,m,len,ans;
char ch[1001];
while(scanf("%d%d",&n,&m)!=EOF)
{
memset(a,0,sizeof(a));
ans=0;
for(i=1;i<=n;i++)
{
scanf("%s",ch);
len=strlen(ch);
for(j=0;j<len;j++)
{
if(ch[j]=='1')
a[j+1]++;
else a[j+1]=0;
b[j+1]=a[j+1];
}
sort(b+1,b+1+m,cmp);
for(j=1;j<=m&&b[j];j++)
if(b[j]*j>ans) ans=b[j]*j;

}
printf("%d\n",ans);
}
return 0;
}