BZOJ 4520 [Cqoi2016]K远点对（KD树）

#include <cstdio>
#include <algorithm>
#include <queue> 
using namespace std;
typedef long long LL;
const int N=200000;
inline int read(){
    int x=0,f=1;char ch=getchar();
    while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘)f=-1;ch=getchar();}
    while(ch>=‘0‘&&ch<=‘9‘){x=x*10+ch-‘0‘;ch=getchar();}
    return x*f;
}
struct data{
    LL dis;
    data(){};
    data(const LL&x){dis=x;}
    bool operator <(const data&x)const{return dis>x.dis;}
}tmp;
priority_queue<data>q;
namespace KD_Tree{
    struct Dot{  
        int d[2],mn[2],mx[2],l,r;  
        Dot(){l=r=0;}  
        Dot(int x,int y){d[0]=x;d[1]=y;l=r=0;}  
        int& operator [] (int x){return d[x];}  
    };  
    int D,dcnt=0,pt[N]; 
    Dot T[N],p[N];
    bool operator<(Dot a,Dot b){return a[D]<b[D];}
    inline void umax(int&a,int b){if(a<b)a=b;}
    inline void umin(int&a,int b){if(a>b)a=b;}
    inline bool cmp(int x,int y){return T[x][D]<T[y][D];}
    inline void up(int x){
        T[x].mn[0]=T[x].mx[0]=T[x][0];  
        T[x].mn[1]=T[x].mx[1]=T[x][1]; 
        if(T[x].l){
            umax(T[x].mx[0],T[T[x].l].mx[0]);
            umin(T[x].mn[0],T[T[x].l].mn[0]);   
            umax(T[x].mx[1],T[T[x].l].mx[1]);
            umin(T[x].mn[1],T[T[x].l].mn[1]);
        }
        if(T[x].r){
            umax(T[x].mx[0],T[T[x].r].mx[0]);
            umin(T[x].mn[0],T[T[x].r].mn[0]);
            umax(T[x].mx[1],T[T[x].r].mx[1]);
            umin(T[x].mn[1],T[T[x].r].mn[1]);
        }
    }
    void AddDot(int x,int y){
        ++dcnt; pt[dcnt]=dcnt;
        p[dcnt][0]=x; p[dcnt][1]=y;
    }
    int build(int l,int r,int now){
    	if(l>r)return 0;
        int mid=(l+r)>>1;
        D=now;
        nth_element(p+l,p+mid,p+r+1);
        T[mid]=p[mid];
        for(int i=0;i<2;i++)T[mid].mn[i]=T[mid].mx[i]=T[mid][i];
        if(l<mid)T[mid].l=build(l,mid-1,now^1);
        if(r>mid)T[mid].r=build(mid+1,r,now^1);
        return up(mid),mid;
    }
    LL sqr(LL x){return x*x;}
    inline LL dist(int x,int px,int py){
        LL dis=0;
        if(!x)return 0;
            dis+=max(sqr(T[x].mn[0]-px),sqr(T[x].mx[0]-px));
            dis+=max(sqr(T[x].mn[1]-py),sqr(T[x].mx[1]-py));
            return dis;
        }
    }
    void query(int x,int px,int py){
        if(!x)return;
        LL dl,dr,d0=sqr(T[x][0]-px)+sqr(T[x][1]-py);
        dl=T[x].l?dist(T[x].l,px,py):0;
        dr=T[x].r?dist(T[x].r,px,py):0;
        if(d0>q.top().dis)q.pop(),q.push(data(d0));
        if(dl>dr){
            if(dl>q.top().dis)query(T[x].l,px,py);
            if(dr>q.top().dis)query(T[x].r,px,py);
        }
        else{
            if(dr>q.top().dis)query(T[x].r,px,py);
            if(dl>q.top().dis)query(T[x].l,px,py);
        }
    }
}
int n,k;
int main(){
    scanf("%d%d",&n,&k);
    for(int i=1;i<=n;i++)KD_Tree::AddDot(read(),read());
    int root=KD_Tree::build(1,n,0);
    for(int i=0;i<k+k;i++)q.push(tmp);
    for(int i=1;i<=n;i++)KD_Tree::query(root,KD_Tree::p[i][0],KD_Tree::p[i][1]);
    printf("%lld\n",q.top().dis);
    return 0;
}