POJ - 2187 Beauty Contest（最遠點對）

http://poj.org/problem?id=2187

題意

給n個坐標，求最遠點對的距離平方值。

分析

模板題，旋轉卡殼求求兩點間距離平方的最大值。

#include<iostream>
#include<cmath>
#include<cstring>
#include<queue>
#include<vector>
#include<cstdio>
#include<algorithm>
#include<map>
#include<set>
#define rep(i,e) for(int i=0;i<(e);i++)
#define rep1(i,e) for(int i=1;i<=(e);i++)
#define repx(i,x,e) for(int i=(x);i<=(e);i++)
#define X first
#define Y second
#define PB push_back
#define MP make_pair
#define mset(var,val) memset(var,val,sizeof(var))
#define scd(a) scanf("%d",&a)
#define scdd(a,b) scanf("%d%d",&a,&b)
#define scddd(a,b,c) scanf("%d%d%d",&a,&b,&c)
#define pd(a) printf("%d\n",a)
#define scl(a) scanf("%lld",&a)
#define scll(a,b) scanf("%lld%lld",&a,&b)
#define sclll(a,b,c) scanf("%lld%lld%lld",&a,&b,&c)
#define IOS ios::sync_with_stdio(false);cin.tie(0)
#define lc idx<<1
#define rc idx<<1|1
#define rson mid+1,r,rc
#define lson l,mid,lc
using namespace std;
typedef long long ll;
template <class T>
void test(T a) {cout<<a<<endl;
}
template <class T,class T2>
void test(T a,T2 b) {cout<<a<<" "<<b<<endl;
}
template <class T,class T2,class T3>
void test(T a,T2 b,T3 c) {cout<<a<<" "<<b<<" "<<c<<endl;
}
const int inf = 0x3f3f3f3f;
const ll INF = 0x3f3f3f3f3f3f3f3fll;
const ll mod = 1e9+7;
int T;
void testcase() {printf("Case %d: ",++T);
}
const int MAXN = 50010;
const int MAXM = 30;
const double PI = acos(-1.0);
const double eps = 1e-7;struct Point{int x,y;Point(int _x=0,int _y=0){x=_x,y=_y;}Point operator -(const Point &b)const{return Point(x-b.x,y-b.y);}int operator ^(const Point &b)const{return x*b.y-y*b.x;}int operator *(const Point &b)const{return x*b.x+y*b.y;}void input(){scanf("%d%d",&x,&y);}
};
int dis2(Point a,Point b){return (a-b)*(a-b);
}
Point List[MAXN];
int Stack[MAXN],top;
bool _cmp(Point p1,Point p2){int tmp=(p1-List[0])^(p2-List[0]);if(tmp>0) return true;else if(tmp==0&&dis2(p1,List[0])<=dis2(p2,List[0])) return true;else return false;
}
void Graham(int n){Point p0;int k=0;p0=List[0];for(int i=1;i<n;i++){if(p0.y>List[i].y||(p0.y==List[i].y&&p0.x>List[i].x)){p0=List[i];k=i;}}swap(List[k],List[0]);sort(List+1,List+n,_cmp);if(n==1){top=1;Stack[0]=0;return;}if(n==2){top=2;Stack[0]=0;Stack[1]=1;return;}Stack[0]=0;Stack[1]=1;top=2;for(int i=2;i<n;i++){while(top>1&&((List[Stack[top-1]]-List[Stack[top-2]])^(List[i]-List[Stack[top-2]]))<=0)top--;Stack[top++]=i;}return;
}
int rotating_calipers(Point p[],int n){int ans=0;Point v;int cur=1;for(int i=0;i<n;i++){v=p[i]-p[(i+1)%n];while((v^(p[(cur+1)%n]-p[cur]))<0)cur=(cur+1)%n;ans=max(ans,max(dis2(p[i],p[cur]),dis2(p[(i+1)%n],p[(cur+1)%n])));}return ans;
}
Point p[MAXN];
int main() {
#ifdef LOCALfreopen("data.in","r",stdin);
#endif // LOCALint n;while(~scanf("%d",&n)){for(int i=0;i<n;i++) List[i].input();Graham(n);for(int i=0;i<top;i++) p[i]=List[Stack[i]];printf("%d\n",rotating_calipers(p,top));}return 0;
}

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