POJ 1118 Lining Up

#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <algorithm>
using namespace std;
struct node
{
    int x,y;
}a[705];
int main()
{
    int n,i,ans,j,f,m;
    while(scanf("%d",&n)!=EOF&&n!=0)
    {
        for(i=1;i<=n;i++)
        {
            scanf("%d%d",&a[i].x,&a[i].y);
        }
        ans=2;
        for(i=1;i<=n;i++)
        {
            for(j=i+1;j<=n;j++)
            {
                //选择两点连成直线
                f=2;
                for(m=j+1;m<=n;m++)//节约时间，避免重复验证
                {
                    if((a[m].x-a[i].x)*(a[m].y-a[j].y)==(a[m].x-a[j].x)*(a[m].y-a[i].y))
                            f++;
                }
                if(f>ans)
                    ans=f;
            }
        }
        printf("%d\n",ans);
    }
    return 0;
}