loj2043 「CQOI2016」K 远点对

k-d tree 裸题………………

#include <algorithm>
#include <iostream>
#include <cstdio>
using namespace std;
typedef long long ll;
int n, k, rot, nowD, din;
ll dui[205];
const ll oo=9e18;
struct Point{
	int d[2], mn[2], mx[2], l, r;
	int & operator[](int x){
		return d[x];
	}
	bool operator<(const Point &x)const{
		return d[nowD]<x.d[nowD];
	}
}p[100005], T;
bool cmp(ll x, ll y){
	return x>y;
}
struct KDTree{
	Point t[100005];
	void pushUp(int k){
		int l=t[k].l, r=t[k].r;
		for(int i=0; i<2; i++){
			t[k].mn[i] = t[k].mx[i] = t[k][i];
			if(l){
				t[k].mn[i] = min(t[k].mn[i], t[l].mn[i]);
				t[k].mx[i] = max(t[k].mx[i], t[l].mx[i]);
			}
			if(r){
				t[k].mn[i] = min(t[k].mn[i], t[r].mn[i]);
				t[k].mx[i] = max(t[k].mx[i], t[r].mx[i]);
			}
		}
	}
	int build(int l, int r, int now){
		nowD = now;
		int mid=(l+r)>>1;
		nth_element(p+l, p+mid, p+r+1);
		t[mid] = p[mid];
		if(l<mid)	t[mid].l = build(l, mid-1, now^1);
		if(mid<r)	t[mid].r = build(mid+1, r, now^1);
		pushUp(mid);
		return mid;
	}
	ll getDis(const Point &u, const Point &v){
		return (ll)(u.d[1]-v.d[1])*(u.d[1]-v.d[1])+(ll)(u.d[0]-v.d[0])*(u.d[0]-v.d[0]);
	}
	ll simDis(int k){
		ll re=0;
		for(int i=0; i<2; i++){
			ll tmp=max(abs(t[k].mn[i]-T[i]), abs(t[k].mx[i]-T[i]));
			re += tmp * tmp;
		}
		return re;
	}
	void query(int k){
		ll d=getDis(t[k], T), disl=-oo, disr=-oo;
		int l=t[k].l, r=t[k].r;
		if(d>dui[1]){
			pop_heap(dui+1, dui+1+din, cmp);
			dui[din] = d;
			push_heap(dui+1, dui+1+din, cmp);
		}
		if(l)	disl = simDis(l);
		if(r)	disr = simDis(r);
		if(disl>disr){
			if(disl>dui[1])	query(l);
			if(disr>dui[1])	query(r);
		}
		else{
			if(disr>dui[1])	query(r);
			if(disl>dui[1])	query(l);
		}
	}
}kdt;
int main(){
	cin>>n>>k;
	k *= 2;
	for(int i=1; i<=n; i++)
		scanf("%d %d", &p[i][0], &p[i][1]);
	rot = kdt.build(1, n, 0);
	while(k--)	dui[++din] = -oo;
	for(int i=1; i<=n; i++){
		T = p[i];
		kdt.query(rot);
	}
	cout<<dui[1]<<endl;
	return 0;
}