poj1696Space Ant（逆时针螺旋形）

链接

贪心做法，没次找最外面的点，也就是相对前面那条线偏转角度最小的点，除第一个点需要找到最下面的点即Y坐标最小，其余的每次进行极角排序。

 #include <iostream>
 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 #include<stdlib.h>
 #include<vector>
 #include<cmath>
 #include<queue>
 #include<set>
 using namespace std;
 #define N 55
 #define LL long long
 #define INF 0xfffffff
 const double eps = 1e-;
 const double pi = acos(-1.0);
 const double inf = ~0u>>;
 int o[];
 struct Point
 {
     int x,y;
     Point(double x=,double y=):x(x),y(y) {}
     int id;
 }p[N];
 int cc;
 typedef Point pointt;
 pointt operator + (Point a,Point b)
 {
     return Point(a.x+b.x,a.y+b.y);
 }
 pointt operator - (Point a,Point b)
 {
     return Point(a.x-b.x,a.y-b.y);
 }
 double dis(Point a)
 {
     return sqrt(1.0*a.x*a.x+a.y*a.y);
 }
 int cross(Point a,Point b)
 {
     return a.x*b.y-a.y*b.x;
 }
 int mul(Point p0,Point p1,Point p2)
 {
     return cross(p1-p0,p2-p0);
 }

 bool cmp(Point a,Point b)
 {
     if(mul(p[cc],a,b)==)
         return dis(a-p[cc])<dis(b-p[]);
     else
         return mul(p[cc],a,b)>;
 }
 int main()
 {
     int t,i,n;
     cin>>t;
     while(t--)
     {
         scanf("%d",&n);
         for(i = ; i <= n ;i++)
         {
             scanf("%d%d%d",&p[i].id,&p[i].x,&p[i].y);
         }
         int tmp = ;
         for(i = ; i <= n; i++)
         if(p[tmp].y>p[i].y)
         {
             tmp = i;
         }
         swap(p[],p[tmp]);
         int g = ;
         o[++g] = p[].id;
         cc = ;
         for(i =  ;i <= n; i++)
         {
             sort(p+i,p+n+,cmp);
             o[++g] = p[i].id;
             cc = i;
         }
         printf("%d",g);
         for(i =  ;i <= g;  i++)
         printf(" %d",o[i]);
         puts("");
     }
     return ;
 }