ural 1207 Median on the Plane

极角排序

 #include <cstdio>
 #include <cstring>
 #include <algorithm>
 #include <cmath>
 #define maxn 30000
 using namespace std;

 struct point
 {
     double x,y;
     int num;
 }p[maxn];
 point pp;
 double cross(const point &a,const point &b,const point &c)
 {
     return (b.x-a.x)*(c.y-a.y)-(b.y-a.y)*(c.x-a.x);
 }
 bool cmp(const point &a,const point &b)
 {
     if(cross(p[],a,b)>) return ;
     else return ;
 }
 int main()
 {
     int n;
     int k=;
     scanf("%d",&n);
     for(int i=; i<n; i++)
     {
         scanf("%lf%lf",&p[i].x,&p[i].y);
         p[i].num=i+;
         if(p[i].y<p[k].y||(p[k].y==p[i].y&&p[i].x<p[k].x)) k=i;
     }
     swap(p[],p[k]);
     sort(p+,p+n,cmp);
     printf("%d %d\n",p[].num,p[n/].num);
     return ;
 }