poj 1696

不错的一题，需要极角排序，看了别人的代码做的。。。。。。计算几何啊~~~

#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>

const double er = 1e-8;
struct point
{
    int index;
    int x,y;
}p[100];
int n;
int res;

int dis(point a,point b)
{
    return sqrt(1.0*(a.x - b.x) * (a.x - b.x) + 1.0*(a.y - b.y)*(a.y - b.y));
}

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

bool cmp(point a,point b)
{
    double temp = outer_product(p[res - 1],a,b);
    if(temp > er) return true;
    temp = temp > 0?temp:(-temp);
    if(temp < er&&dis(a,p[res - 1]) < dis(b,p[res -1]))
        return true;
    return false;
}

int main()
{
    int cas;
    scanf("%d",&cas);
    while(cas --)
    {
        scanf("%d",&n);
        for(int i = 0;i < n;i ++)
        {
            scanf("%d%d%d",&p[i].index,&p[i].x,&p[i].y);
            if(p[i].y < p[0].y) std::swap(p[i],p[0]);
            if(p[i].y == p[0].y)
            {
                if(p[i].x <p[0].x)
                    std::swap(p[i],p[0]);
            }
        }
        printf("%d %d",n,p[0].index);

        for(res = 1;res < n;res ++)
        {
            std::sort(p+res,p+n,cmp);
            printf(" %d",p[res].index);
        }
        printf("\n");
    }

    return 0;
}