叉积判断 POJ1696

 // 叉积判断 POJ1696

 #include <iostream>
 #include <algorithm>
 #include <cstring>
 #include <cstdio>
 #include <vector>
 #include <cmath>
 #include <map>
 using namespace std;
 #define LL long long
 typedef pair<int,int> pii;
 const double inf = 123456789012345.0;
 const int MOD = ;
 const int N = 2e5+;
 const int maxx = ;
 #define clc(a,b) memset(a,b,sizeof(a))
 const double eps = 1e-;
 void fre() {freopen("in.txt","r",stdin);}
 void freout() {freopen("out.txt","w",stdout);}
 inline int read() {int x=,f=;char ch=getchar();while(ch>''||ch<'') {if(ch=='-') f=-; ch=getchar();}while(ch>=''&&ch<='') {x=x*+ch-'';ch=getchar();}return x*f;}

 int sgn(double x){
     if(fabs(x) < eps)return ;
     if(x < )return -;
     else return ;
 }

 struct Point{
     double x,y;
     int index;
     Point(){}
     Point(double _x,double _y){
         x = _x;y = _y;
     }
     Point operator -(const Point &b)const{
         return Point(x - b.x,y - b.y);
     }
     double operator ^(const Point &b)const{
         return x*b.y - y*b.x;
     }
     double operator *(const Point &b)const{
         return x*b.x + y*b.y;
     }
 };

 double dist(Point a,Point b){
     return sqrt((a-b)*(a-b));
 }

 int pos;
 Point p[];
 bool cmp(Point a,Point b){
     double tmp=(a-p[pos])^(b-p[pos]);
     if(sgn(tmp)==){
         return dist(a,p[pos])<dist(b,p[pos]);
     }
     else if(sgn(tmp)<) return false;
     else return true;
 }

 int main(){
     int T,n;
     scanf("%d",&T);
     while(T--){
         scanf("%d",&n);
         for(int i=;i<n;i++){
             scanf("%d%lf%lf",&p[i].index,&p[i].x,&p[i].y);
             if(p[i].y<p[].y||(p[i].y==p[].y&&p[i].x<p[].x)){
                 swap(p[i],p[]);
             }
         }
         pos=;
         for(int i=;i<n;i++){
             sort(p+i,p+n,cmp);
             pos++;
         }
         printf("%d",n);
         for(int i=;i<n;i++)
             printf(" %d",p[i].index);
         printf("\n");
     }
     return ;
 }