【kd-tree】CDOJ - 1170 - 红与蓝

#include<cstdio>
#include<cmath>
#include<algorithm>
using namespace std;
#define N 100010
#define EPS 0.00000001
#define INF 1000000000000000007.0
#define KD 2
int qp[KD];
double disn;
int n,root;
bool dn;
double sqr(int x)
{
	return (double)x*(double)x;
}
int Abs(int x)
{
	return x<0 ? (-x) : x;
}
struct Node
{
    int minn[KD],maxx[KD],p[KD];
    int ch[2];
    void Init()
      {
        for(int i=0;i<KD;++i)
          minn[i]=maxx[i]=p[i];
      }
    bool CheckIn()
      {
      	for(int i=0;i<KD;++i)
      	  if(!(minn[i]<=qp[i] && qp[i]<=maxx[i]))
      	    return 0;
      	return 1;
      }
    int Dis()
      {
      	if(CheckIn())
      	  return 0;
        int res=2147483647;
        res=min(res,Abs(minn[0]-qp[0]));
        res=min(res,Abs(maxx[0]-qp[0]));
        res=min(res,Abs(minn[1]-qp[1]));
        res=min(res,Abs(maxx[1]-qp[1]));
        return res;
      }
}T[N<<1];
void Update(int rt)
{
    for(int i=0;i<2;++i)
      if(T[rt].ch[i])
        for(int j=0;j<KD;++j)
          {
            T[rt].minn[j]=min(T[rt].minn[j],T[T[rt].ch[i]].minn[j]);
            T[rt].maxx[j]=max(T[rt].maxx[j],T[T[rt].ch[i]].maxx[j]);
          }
}
bool operator < (const Node &a,const Node &b)
{
    return a.p[dn]!=b.p[dn] ? a.p[dn]<b.p[dn] : a.p[dn^1]<b.p[dn^1];
}
int Buildtree(int l=1,int r=n,bool d=0)
{
    dn=d;
    int m=(l+r>>1);
    nth_element(T+l,T+m,T+r+1);
    T[m].Init();
    if(l!=m) T[m].ch[0]=Buildtree(l,m-1,d^1);
    if(m!=r) T[m].ch[1]=Buildtree(m+1,r,d^1);
    Update(m);
    return m;
}
double Dis(int a[],int b[])
{
    return sqrt(sqr(a[0]-b[0])+sqr(a[1]-b[1]));
}
void Query(int rt=root)
{
    disn=min(disn,Dis(T[rt].p,qp));
    int dd[2];
    for(int i=0;i<2;i++)
      if(T[rt].ch[i])
        dd[i]=T[T[rt].ch[i]].Dis();
      else dd[i]=2147483647;
    bool f=(dd[0]<=dd[1]);
    if((double)dd[!f]-disn<(-EPS)) Query(T[rt].ch[!f]);
    if((double)dd[f]-disn<(-EPS)) Query(T[rt].ch[f]);
}
int main()
{
//	freopen("k.in","r",stdin);
//	freopen("k.out","w",stdout);
    scanf("%d",&n);
    for(int i=1;i<=n;++i)
      scanf("%d%d",&T[i].p[0],&T[i].p[1]);
    root=(1+n>>1);
    Buildtree();
    disn=INF;
    for(int i=1;i<=n;++i)
      {
        scanf("%d%d",&qp[0],&qp[1]);
        Query();
      }
    printf("%.3lf\n",disn);
    return 0;
}