POJ 2606

 #include<iostream>
 #include<set>
 #include<stdio.h>
 #include<math.h>
 #include<algorithm>
 #define MAXN 705
 using namespace std;
 int num;
 double p[MAXN][];
 double a[MAXN*MAXN];
 set<int> coll;
 set<int>::iterator pos;
 multiset<int> coll_main;
 int main()
 {
     //freopen("acm.acm","r",stdin);
     int i;
     int max;
     int j;
     int k;
     int t;
     double value;
     int num;
     double s2;
     scanf("%d",&num);
     max = ;
     for(i = ; i < num; ++ i)
     {
         scanf("%lf%lf",&p[i][],&p[i][]);
     }
     for(i = ; i < num; ++ i)
     {
         k = ;
         for(j = ; j < num; ++ j)
         {
             if(i != j)
             {
                 value = (p[i][] - p[j][]) / (p[i][] - p[j][]);
                 a[k] = value;
                 ++ k;
             }
         }
         sort(a,a + k);
         s2 = a[];
         j = ;
         for(t = ; t < k; ++ t)
         {
             if(a[t] == s2)
                 ++ j;
             else
             {
                 if(j > max)
                 {
                     max = j;
                 }
                 s2 = a[t];
                 -- t;
                 j = ;
             }
         }
         if(j > max)
             max = j;
     }
     ++max;
     cout<<max<<endl;
 }