POJ_2187_Beauty Contest(凸包+暴力)

#include<cstring>
#include<cmath>
#include<cstdio>
#include<algorithm>
#include<iostream>
using namespace std;
int n;
struct point{
int x,y;
}pnt[60000],res[60000];

bool mult(point sp,point ep,point op){
return (sp.x-op.x)*(ep.y-op.y)>=(ep.x-op.x)*(sp.y-op.y);
}
bool operator < (const point &l,const point &r){
return l.y<r.y || (l.y==r.y && l.x<r.x);
}
int graham(){
int i,len,k=0,top=1;
sort(pnt,pnt+n);
if(n==0) return 0; res[0] = pnt[0];
if(n==1) return 1; res[1] = pnt[1];
if(n==2) return 2; res[2] = pnt[2];
for(i=2;i<n;i++){
while(top && mult(pnt[i],res[top],res[top-1])) top--;
res[++top] = pnt[i];
}
len=top; res[++top] = pnt[n-2];
for(i=n-3;i>=0;i--){
while(top!=len && mult(pnt[i],res[top],res[top-1]))
top--;
res[++top] = pnt[i];
}
return top;
}

int dis(point a,point b){
return (a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y);
}

int main(){
while(~scanf("%d",&n)){
int MAXN=0;
for(int i=0;i<n;i++){
scanf("%d%d",&pnt[i].x,&pnt[i].y);
}
int top=graham();
for(int i=0;i<top;i++){
for(int j=0;j<top;j++){
if(i==j) continue;
MAXN = max(MAXN,dis(res[i],res[j]));
}
}
printf("%d\n",MAXN);
}
return 0;
}