BZOJ 4520: [Cqoi2016]K远点对 KDtree + 估价函数 + 堆

Code:

#include<bits/stdc++.h>
#define ll long long 
#define maxn 200000 
#define inf 100000000000000 
#define lson (t[x].ch[0])
#define rson (t[x].ch[1]) 
#define mid ((l+r)>>1) 
using namespace std;
void debug()
{
    printf("no_problem\n");   
}    
int n,K,d,root; 
void setIO(string s)
{
    string in=s+".in"; 
    freopen(in.c_str(),"r",stdin);  
}
priority_queue<ll,vector<ll>, greater<ll> >Q; 
struct Node
{
    int p[2],ch[2],minv[2],maxv[2]; 
}t[maxn],T; 
bool cmp(Node a,Node b)
{
    return a.p[d]==b.p[d]?a.p[d^1]<b.p[d^1]:a.p[d]<b.p[d]; 
}
void pushup(int x,int y)
{
    t[x].minv[0]=min(t[x].minv[0],t[y].minv[0]); 
    t[x].maxv[0]=max(t[x].maxv[0],t[y].maxv[0]); 
    t[x].minv[1]=min(t[x].minv[1],t[y].minv[1]); 
    t[x].maxv[1]=max(t[x].maxv[1],t[y].maxv[1]);   
}
int build(int l,int r,int o)
{
    d=o;
    nth_element(t+l,t+mid,t+1+r,cmp); 
    t[mid].minv[0]=t[mid].maxv[0]=t[mid].p[0]; 
    t[mid].minv[1]=t[mid].maxv[1]=t[mid].p[1]; 
    t[mid].ch[0]=t[mid].ch[1]=0; 
    if(mid>l)
    {
        t[mid].ch[0]=build(l,mid-1,o^1); 
        pushup(mid,t[mid].ch[0]); 
    }
    if(r>mid)
    {
        t[mid].ch[1]=build(mid+1,r,o^1); 
        pushup(mid,t[mid].ch[1]); 
    }
    return mid; 
} 
ll sq(ll x)
{ 
    return x * x; 
}
ll getmax(int x)
{
    ll ans=0;
    for(int i=0;i<2;++i)
    {
        ans+=max( sq(1ll*(t[x].minv[i]-T.p[i])), sq(1ll*(t[x].maxv[i]-T.p[i])) ); 
    }
    return ans; 
}
void solve(int x,int x1,int y1)
{
    ll dn=getmax(x), cur=sq(1ll*(t[x].p[0]-x1)) + sq(1ll*(t[x].p[1]-y1));      
    if(dn <= Q.top()) return;  
    if(cur>Q.top())           
    {
        Q.pop(); 
        Q.push(cur); 
    }                       
    ll dl=lson ? getmax(lson) : -inf; 
    ll dr=rson ? getmax(rson) : -inf; 
    if(dl>dr)
    {
        if(dl > Q.top()) solve(lson, x1, y1);   
        if(dr > Q.top()) solve(rson, x1, y1); 
    }
    else 
    {
        if(dr > Q.top()) solve(rson, x1, y1); 
        if(dl > Q.top()) solve(lson, x1, y1); 
    }
}
int main()
{
    // setIO("input");
    scanf("%d%d",&n,&K); 
    K<<=1;  
    for(int i=1;i<=n;++i) scanf("%d%d",&t[i].p[0],&t[i].p[1]);  
    root=build(1,n,0); 
    for(int i=1;i<=K;++i) Q.push(0); 
    for(int i=1;i<=n;++i)
    {
        T.p[0]=t[i].p[0]; 
        T.p[1]=t[i].p[1]; 
        solve(root,T.p[0],T.p[1]);  
    }   
    printf("%lld\n",Q.top()); 
    return 0;    
}