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。

 1 #include <iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<algorithm>
 5 #include<stdlib.h>
 6 #include<vector>
 7 #include<cmath>
 8 #include<queue>
 9 #include<set>
10 using namespace std;
11 #define N 55
12 #define LL long long
13 #define INF 0xfffffff
14 const double eps = 1e-8;
15 const double pi = acos(-1.0);
16 const double inf = ~0u>>2;
17 int o[55];
18 struct Point
19 {
20     int x,y;
21     Point(double x=0,double y=0):x(x),y(y) {}
22     int id;
23 }p[N];
24 int cc;
25 typedef Point pointt;
26 pointt operator + (Point a,Point b)
27 {
28     return Point(a.x+b.x,a.y+b.y);
29 }
30 pointt operator - (Point a,Point b)
31 {
32     return Point(a.x-b.x,a.y-b.y);
33 }
34 double dis(Point a)
35 {
36     return sqrt(1.0*a.x*a.x+a.y*a.y);
37 }
38 int cross(Point a,Point b)
39 {
40     return a.x*b.y-a.y*b.x;
41 }
42 int mul(Point p0,Point p1,Point p2)
43 {
44     return cross(p1-p0,p2-p0);
45 }
46
47 bool cmp(Point a,Point b)
48 {
49     if(mul(p[cc],a,b)==0)
50         return dis(a-p[cc])<dis(b-p[1]);
51     else
52         return mul(p[cc],a,b)>0;
53 }
54 int main()
55 {
56     int t,i,n;
57     cin>>t;
58     while(t--)
59     {
60         scanf("%d",&n);
61         for(i = 1; i <= n ;i++)
62         {
63             scanf("%d%d%d",&p[i].id,&p[i].x,&p[i].y);
64         }
65         int tmp = 1;
66         for(i = 2; i <= n; i++)
67         if(p[tmp].y>p[i].y)
68         {
69             tmp = i;
70         }
71         swap(p[1],p[tmp]);
72         int g = 0;
73         o[++g] = p[1].id;
74         cc = 1;
75         for(i = 2 ;i <= n; i++)
76         {
77             sort(p+i,p+n+1,cmp);
78             o[++g] = p[i].id;
79             cc = i;
80         }
81         printf("%d",g);
82         for(i = 1 ;i <= g;  i++)
83         printf(" %d",o[i]);
84         puts("");
85     }
86     return 0;
87 }

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