POJ 1696

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <queue>
#include <cmath>

using namespace std;
const double inf=10000000;
const double eps=0.00000001;
struct point {
	double x,y;
	int num;
}p[60];

bool vis[60];
queue<int>que;
struct vect{
	double x,y;
};

double dist(point a,point b){
	return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
}

double cross(point a,point b,point c,point d){
	return (a.x-b.x)*(c.y-d.y)-(a.y-b.y)*(c.x-d.x);
}

int n;
int main(){
	int t;
	scanf("%d",&t); double a,b;
	while(t--){
		scanf("%d",&n);
		point start; start.x=inf; start.y=inf; int dep;
		for(int i=0;i<n;i++){
			scanf("%d%lf%lf",&p[i].num,&p[i].x,&p[i].y);
			if(p[i].y<start.y){
				start.x=p[i].x; start.y=p[i].y; start.num=p[i].num;
				dep=i;
			}
			else if(p[i].y==start.y){
				if(p[i].x<start.x){
					start.x=p[i].x; start.num=p[i].num;
					dep=i;
				}
			}
		}
	//	cout<<start.x<<‘ ‘<<start.y<<endl;
		point last; last.x=0; last.y=start.y;
		que.push(start.num);
		memset(vis,false,sizeof(vis));
		vis[dep]=true; point tmp;
		while(true){
			bool flag=false;
			for(int i=0;i<n;i++){
				if(vis[i]==false){
					if(cross(start,last,p[i],start)>=0){
						tmp=p[i];
						dep=i;
						flag=true;
						break;
					}
				}
			}
		//	cout<<dep<<"YES"<<endl;
			if(!flag) break;
			for(int i=0;i<n;i++){
				if(vis[i]==false){
					if(cross(start,last,p[i],start)<0) continue;
					double res=cross(tmp,start,p[i],start);
					if(res<0){
						tmp=p[i];
						dep=i;
					}
					else if(res==0){
						if(dist(p[i],start)+eps<dist(tmp,start)){
							tmp=p[i];
							dep=i;
						}
					}
				}
			}
			que.push(tmp.num);
			//cout<<dep<<endl;
			vis[dep]=true;
			last=start;
			start=tmp;
		}
		printf("%d",n);
		for(int i=0;i<n;i++){
			printf(" %d",que.front());
			que.pop();
		}
		printf("\n");
	}
	return 0;
}