【hdu4347】The Closest M Points 【KD树模板】

题意

一个k维空间，给出n个点的坐标，给出t个询问，每个询问给出一个点的坐标和一个m。对于每个询问找出跟这个点最接近的m个点

分析

kd树的模板题。

 #include <cstdio>
 #include <cstring>
 #include <iostream>
 #include <algorithm>
 #include <queue>
 
 using namespace std;
 typedef long long LL;
 const int maxn=;
 const int K=;
 int num,nownum,m;
 LL ans;
 struct kdNode{
     LL x[K];
     int div;
     bool lef;
 }Ans[];
 struct Node{
     kdNode a;
     LL dis;
     bool operator <(const Node &a)const{
         return dis<a.dis;
     }
     Node(){}
     Node(kdNode &tmp,LL d){
         a=tmp;
         dis=d;
     }
 };
 int cmpNo;
 bool cmp(kdNode a,kdNode b){
     return a.x[cmpNo]<b.x[cmpNo];
 }
 inline LL max(LL a,LL b){//why?
     return a>b?a:b;
 }
 kdNode p[maxn],q;
 LL dis(kdNode a,kdNode b,int k){
     LL res=;
     for(int i=;i<k;i++){
         res+=(a.x[i]-b.x[i])*(a.x[i]-b.x[i]);
     }
     return res;
 }
 priority_queue<Node>qq;
 void buildKD(int l,int r,kdNode* p,int d,int k){
     if(l>r)return ;
     int m=(l+r)/;
     cmpNo=d;
     nth_element(p+l,p+m,p+r+,cmp);
     p[m].div=d;
     if(l==r){
         p[m].lef=;
         return ;
     }
     buildKD(l,m-,p,(d+)%k,k);
     buildKD(m+,r,p,(d+)%k,k);
 }
 void findkd(int l,int r,kdNode& tar,kdNode* p,int k){
     if(l>r)return;
     int m=(l+r)/;
     LL d=dis(p[m],tar,k);
     if(p[m].lef){
         if(nownum<num){
             nownum++;
             ans=max(ans,d);
             qq.push(Node(p[m],d));
         }
         else if(ans>d){
             qq.pop();
             qq.push(Node(p[m],d));
             ans=qq.top().dis;
         }
         return;
     }
     LL t=tar.x[p[m].div]-p[m].x[p[m].div];
     if(t>){
         findkd(m+,r,tar,p,k);
         if(nownum<num){
             qq.push(Node(p[m],d));
             nownum++;
             ans=qq.top().dis;
             findkd(l,m-,tar,p,k);
         }else{
             if(ans>d){
                 qq.pop();
                 qq.push(Node(p[m],d));
                 ans=qq.top().dis;
             }
             if(ans>t*t)
                 findkd(l,m-,tar,p,k);
         }
     }else{
         findkd(l,m-,tar,p,k);
         if(nownum<num){
             qq.push(Node(p[m],d));
             nownum++;
             ans=qq.top().dis;
             findkd(m+,r,tar,p,k);
         }else{
             if(ans>d){
                 qq.pop();
                 qq.push(Node(p[m],d));
                 ans=qq.top().dis;
             }
             if(ans>t*t){
                 findkd(m+,r,tar,p,k);
             }
         }
     }
 }
 
 int n,k;
 int main(){
     while(scanf("%d%d",&n,&k)==){
         for(int i=;i<n;i++){
             for(int j=;j<k;j++){
                 scanf("%lld",&p[i].x[j]);
             }
             p[i].lef=;
         }
         buildKD(,n-,p,k-,k);
         int t;
         scanf("%d",&t);
         for(int i=;i<=t;i++){
             ans=-;
             nownum=;
             for(int j=;j<k;j++){
                 scanf("%lld",&q.x[j]);
             }
             while(!qq.empty())qq.pop();
             scanf("%d",&num);
             findkd(,n-,q,p,k);
             for(int j=;j<=num;j++){
                 Ans[j]=qq.top().a;
                 qq.pop();
             }
             printf("the closest %d points are:\n",num);
             for(int j=num;j>=;j--){
                 for(int kk=;kk<k;kk++){
                     if(kk==)
                         printf("%lld",Ans[j].x[kk]);
                     else
                         printf(" %lld",Ans[j].x[kk]);
                 }
                 printf("\n");
             }
         }
     }
 return ;
 }