hdu 5020 求3点共线的组合数

http://acm.hdu.edu.cn/showproblem.php?pid=5020

求3点共线的组合数

极角排序然后组合数相加

#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>
#include <string>
#include <queue>
#include <vector>
#include<map>
#include <iostream>
#include <algorithm>
using namespace std;
#define RD(x) scanf("%d",&x)
#define RD2(x,y) scanf("%d%d",&x,&y)
#define clr0(x) memset(x,0,sizeof(x))
typedef long long LL;
typedef pair<int,int> pii;
const double INF=2100000000;

struct point
{
    int x,y;
}p[1010];
int cmp(point a,point b)
{
    return (a.x == b.x && a.y < b.y) || a.x < b.x;
}
int gcd(int a,int b)
{
    return b == 0? a:gcd(b,a%b);
}
map <pii,int> hash;
int main()
{
    int _,n;
    RD(_);
    while(_--){
        RD(n);
        for(int i = 0;i < n;++i)
            RD2(p[i].x,p[i].y);
        sort(p,p+n,cmp);

        map<pii,int>::iterator it;
        int ans = 0;
        for(int i = 0;i < n - 1;++i){
            hash.clear();
            for(int j = i+1;j < n;++j){
                int dx = p[j].x - p[i].x,dy = p[j].y - p[i].y;
                int g = gcd(dx,dy);
                dx /= g,dy /= g;
                hash[make_pair(dx,dy)]++;
            }
            for(it = hash.begin();it != hash.end();++it){
                int x = it->second;
                ans += x*(x - 1)/2;
            }
        }
        cout<<ans<<endl;
    }
    return 0 ;
}