poj2187 Beauty Contest

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求平面上距离最远的两个点距离的平方。

凸包，旋转卡壳。

抄板选手的日常。

//Achen
#include<algorithm>
#include<iostream>
#include<cstring>
#include<cstdlib>
#include<vector>
#include<cstdio>
#include<queue>
#include<cmath>
typedef long long LL;
typedef double db;
const db eps=1e-10;
const int N=50007;
using namespace std;
int n;

template<typename T>void read(T &x)  {
    char ch=getchar(); x=0; T f=1;
    while(ch!='-'&&(ch<'0'||ch>'9')) ch=getchar();
    if(ch=='-') f=-1,ch=getchar();
    for(;ch>='0'&&ch<='9';ch=getchar()) x=x*10+ch-'0'; x*=f;
}

struct pt {
    db x,y;
    pt(db x=0,db y=0):x(x),y(y){} 
}p[N],q[N]; 
typedef  pt vc; 

vc operator + (vc A,vc B) { return vc(A.x+B.x,A.y+B.y);}
vc operator - (vc A,vc B) { return vc(A.x-B.x,A.y-B.y);}
bool operator <(const vc&A,const vc&B) { return A.x<B.x||(A.x==B.x&&A.y<B.y);}
int dcmp(double x) { if(fabs(x)<eps) return 0; else return x<0?-1:1;}
bool operator == (const vc&A,const vc&B) { return dcmp(A.x-B.x)==0&&dcmp(A.y-B.y)==0; }

db dot(vc A,vc B) { return A.x*B.x+A.y*B.y; }
db length(vc A) { return dot(A,A); }
db cross(vc A,vc B) { return A.x*B.y-A.y*B.x; }

bool cmp(const pt &A,const pt&B) {
    return dcmp(cross(A-p[1],B-p[1]))==0?length(A-p[1])<length(B-p[1]):cross(A-p[1],B-p[1])>0;
}

int top;
void graham() {
    for(int i=2;i<=n;i++) if(p[i]<p[1]) swap(p[i],p[1]);
    sort(p+2,p+n+1,cmp);
    q[++top]=p[1]; q[++top]=p[2];
    for(int i=3;i<=n;i++) {
        while(top>1&&cross(q[top]-q[top-1],p[i]-q[top-1])<eps) top--;
        q[++top]=p[i];
    }
}

db RC() {
    q[top+1]=q[1];
    int now=2; 
    db res=0;
    for(int i=1;i<=top;i++) {
        while(cross(q[i+1]-q[i],q[now]-q[i])<cross(q[i+1]-q[i],q[now+1]-q[i])) {
            now++; if(now==top+1) now=1;
        }    
        res=max(res,length(q[now]-q[i]));
    }
    return res;
}

int main() {
    read(n);
    for(int i=1;i<=n;i++) { read(p[i].x); read(p[i].y); }
    graham();
    printf("%d
",(int)RC());
    return 0;
}