Beauty Contest POJ

Beauty Contest

POJ - 2187

题意：问凸包的直径．

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
const int inf=1e9+10;
const int maxn=50010;

struct Node{
    int x,y;
    bool operator <(const Node &a)const{
        return x<a.x||(x==a.x&&y<a.y);
    }
    Node operator -(Node &a){
        return Node{x-a.x,y-a.y};
    }
}p[maxn],ch[maxn];
int cross(Node a,Node b){
    return a.x*b.y-a.y*b.x;
}
double getlen(Node a){
    return a.x*a.x+a.y*a.y;
}

int ConvexHull(int n){
    sort(p,p+n);
    int m=0;
    for(int i=0;i<n;i++){
        while(m>1&&cross(ch[m-1]-ch[m-2],p[i]-ch[m-2])<=0) m--;
        ch[m++]=p[i];
    }
    int k=m;
    for(int i=n-2;i>=0;i--){
        while(m>k&&cross(ch[m-1]-ch[m-2],p[i]-ch[m-2])<=0) m--;
        ch[m++]=p[i];
    }
    if(n>1) m--;
    return m;
}

//RotatrCalipers
double RC(int n){
    double ans=-inf;
    ch[n]=ch[0];
    int q=1;
    for(int i=0;i<n;i++){
        while(cross(ch[i+1]-ch[i],ch[q]-ch[i])<cross(ch[i+1]-ch[i],ch[q+1]-ch[i])) q=(q+1)%n;
        ans=max(ans,max(getlen(ch[q]-ch[i]),getlen(ch[q+1]-ch[i+1])));
    }
    return ans;
}

int main(){
    int n;
   // freopen("in.txt","r",stdin);
    while(scanf("%d",&n)!=EOF){
        for(int i=0;i<n;i++) scanf("%d%d",&p[i].x,&p[i].y);
        int m=ConvexHull(n);
        double ans=RC(m);
        printf("%.0f
",ans);
    }
}