链接：http://poj.org/problem?id=2187
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(){;}