poj2187 Beauty Contest 旋转卡壳

题意：找到一个多边形的直径。
裸的旋转卡壳……连坑点都没有……不说什么，板子献上……
 1 #include<iostream>
 2 #include<cstdio>
 3 #include<algorithm>
 4 #include<cstring>
 5 #include<cmath>
 6 using namespace std;
 7 const int maxn=50005,inf =0x3f3f3f3f;
 8 struct point
 9 {
10     int x,y;
11 }p[maxn];
12 int n,s[maxn];
13 int multi(point a,point b,point c)
14 {
15     return (b.x-a.x)*(c.y-a.y)-(b.y-a.y)*(c.x-a.x);
16 }
17 int dis(point a,point b)
18 {
19     return (b.x-a.x)*(b.x-a.x)+(b.y-a.y)*(b.y-a.y);
20 }
21 int cmp(point a,point b)
22 {
23     int tmp=multi(p[1],a,b);
24     if(!tmp)return dis(p[1],a)<dis(p[1],b);
25     return tmp>0;
26 }
27 int haha()
28 {
29     int j;
30     int res=0;point begin;int top=-1;
31     scanf("%d",&n);begin.x=begin.y=10005;
32     for(int i=1;i<=n;i++)
33     {
34         scanf("%d %d",&p[i].x,&p[i].y);
35         if(p[i].y<begin.y)begin=p[i],j=i;
36         else if(p[i].y==begin.y&&p[i].x<begin.x)begin=p[i],j=i;
37     }
38     if(n==2)
39     {
40         printf("%d
",dis(p[1],p[2]));
41         return 0;
42     }
43     p[j]=p[1],p[1]=begin;
44     sort(p+2,p+n+1,cmp);
45     s[++top]=1,s[++top]=2;
46     for(int i=3;i<=n;i++)
47     {
48         while(top>0&&multi(p[s[top-1]],p[s[top]],p[i])<=0)top--;
49         s[++top]=i;
50     }
51     j=1,s[++top]=1;
52     for(int i=0;i<top;i++)
53     {
54         while(multi(p[s[i]],p[s[i+1]],p[s[j+1]])>multi(p[s[i]],p[s[i+1]],p[s[j]]))j=(j+1)%top;
55         res=max(res,dis(p[s[i]],p[s[j]]));
56     }
57     printf("%d
",res);
58     return 0;
59 }
60 int sb=haha();
61 int main(){;}
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