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 = 998244353;
const int N = 2e5+10;
const int maxx = 200010; 
#define clc(a,b) memset(a,b,sizeof(a))
const double eps = 1e-8;
void fre() {freopen("in.txt","r",stdin);}
void freout() {freopen("out.txt","w",stdout);}
inline int read() {int x=0,f=1;char ch=getchar();while(ch>'9'||ch<'0') {if(ch=='-') f=-1; ch=getchar();}while(ch>='0'&&ch<='9') {x=x*10+ch-'0';ch=getchar();}return x*f;}

int sgn(double x){
    if(fabs(x) < eps)return 0;
    if(x < 0)return -1;
    else return 1;
}

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[110];
bool cmp(Point a,Point b){
    double tmp=(a-p[pos])^(b-p[pos]);
    if(sgn(tmp)==0){
        return dist(a,p[pos])<dist(b,p[pos]);
    }
    else if(sgn(tmp)<0) return false;
    else return true;
}

int main(){
    int T,n;
    scanf("%d",&T);
    while(T--){
        scanf("%d",&n);
        for(int i=0;i<n;i++){
            scanf("%d%lf%lf",&p[i].index,&p[i].x,&p[i].y);
            if(p[i].y<p[0].y||(p[i].y==p[0].y&&p[i].x<p[0].x)){
                swap(p[i],p[0]);
            }
        }
        pos=0;
        for(int i=0;i<n;i++){
            sort(p+i,p+n,cmp);
            pos++;
        }
        printf("%d",n);
        for(int i=0;i<n;i++)
            printf(" %d",p[i].index);
        printf("
");
    }
    return 0;
}