OJ-Problems-Source/HDOJ/5020_autoAC.cpp

#include <iostream>
#include <cstring>
#include <string>
#include <algorithm>
#include <cmath>
#include <vector>
#include <set>
#include <queue>
#include <map>
using namespace std;
#define INF 1e9
#define maxn 1010
#define rep(i,x,y) for(int i=x;i<=y;i++)
#define mset(x) memset(x,0,sizeof(x))
typedef pair<int, int> pii;
int t, n;
struct point{
    int x, y;
}p[maxn];
map< pii, int > tb;
map< pii, int >::iterator it;
bool cmp(const point& a, const point& b){
    return (a.x==b.x&&a.y<b.y) || a.x<b.x;
}
int gcd(int a, int b){
    if(b==0) return a;
    return gcd(b, a%b);
}
int main(){
    cin>>t;
    while(t--){
        cin>>n;
        rep(i,1,n)    scanf("%d%d", &p[i].x, &p[i].y);
        sort(p+1, p+n+1, cmp);                
        int cnt=0;
        rep(i,1,n-2){
            tb.clear();
            rep(j,i+1,n){
                int dx = p[j].x - p[i].x;
                int dy = p[j].y - p[i].y;
                int d = gcd(dx, dy);
                dx = dx/d;
                dy = dy/d;
                tb[make_pair(dx,dy)]++;
            }
            for(it=tb.begin(); it!=tb.end(); it++){
                int x = it->second;
                if(x>=2)    
                    cnt += x*(x-1)/2; //C(x,2)
            }
        }
        cout<<cnt<<endl;
    }
    return 0;
}