HDU 2830 Matrix Swapping II

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<limits.h>
using namespace std;
int n,m;
char str[1100];
int num[1100],sum[1100];
int cmp(int a,int b)
{
    return a>b;
}
int main()
{
    while(~scanf("%d%d",&n,&m))
    {
        getchar();
        char ch;
        int ans=0;
        memset(num,0,sizeof(num));
        for(int i=1;i<=n;i++)
        {
            for(int j=1;j<=m;j++)
            {
                scanf("%c",&ch);
                if(ch=='1')
                    num[j]++;
                else
                    num[j]=0;
                sum[j]=num[j];
            }
            sort(sum+1,sum+m+1,cmp);
            for(int i=1;i<=m;i++)
                 ans=max(ans,sum[i]*i);
            getchar();
        }
        printf("%d\n",ans);
    }
    return 0;
}