hdu 4251 划分树

思路：裸的划分树

#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cmath>
#include<cstring>
#define Maxn 100010
#define lson(x) x<<1
#define rson(x) x<<1|1
#define mid ((tree[po].l+tree[po].r)>>1)
using namespace std;
int val[20][Maxn],toLeft[20][Maxn],sorted[Maxn];
struct Tree{
    int l,r;
}tree[Maxn*4];
void BuildTree(int l,int r,int dep,int po)
{
    tree[po].l=l,tree[po].r=r;
    if(l==r)
        return ;
    int same=mid-l+1,i;
    for(i=l;i<=r;i++)
        if(val[dep][i]<sorted[mid])
        same--;
    int lpos=l,rpos=mid+1;
    for(i=l;i<=r;i++){
        if(i==l)
        toLeft[dep][i]=0;
        else
        toLeft[dep][i]=toLeft[dep][i-1];
        if(val[dep][i]<sorted[mid])
            toLeft[dep][i]++,val[dep+1][lpos++]=val[dep][i];
        else
        if(val[dep][i]>sorted[mid])
            val[dep+1][rpos++]=val[dep][i];
        else
            if(same)
            toLeft[dep][i]++,val[dep+1][lpos++]=val[dep][i],same--;
            else
            val[dep+1][rpos++]=val[dep][i];
    }
    BuildTree(l,mid,dep+1,lson(po));
    BuildTree(mid+1,r,dep+1,rson(po));
}
int query(int l,int r,int k,int dep,int po)
{
    if(l==r)
        return val[dep][l];
    int vd,invd;
    if(l==tree[po].l){
        vd=toLeft[dep][r];
        invd=0;
    }
    else{
        vd=toLeft[dep][r]-toLeft[dep][l-1];
        invd=toLeft[dep][l-1];
    }
    if(vd>=k){
        int newl=invd+tree[po].l;
        int newr=invd+vd+tree[po].l-1;
        return query(newl,newr,k,dep+1,lson(po));
    }
    else{
        int ss=l-tree[po].l-invd;
        int s=r-l+1-vd;
        int newl=mid+ss+1;
        int newr=mid+ss+s;
        return query(newl,newr,k-vd,dep+1,rson(po));
    }
}
int main()
{
    int n,m,i,j,l,r,Case=0,t,x;
    while(scanf("%d",&n)!=EOF)
    {
        for(i=1;i<=n;i++){
            scanf("%d",val[0]+i);
            sorted[i]=val[0][i];
        }
        sort(sorted+1,sorted+1+n);
        BuildTree(1,n,0,1);
        printf("Case %d:\n",++Case);
        scanf("%d",&m);
        for(i=1;i<=m;i++){
            scanf("%d%d",&l,&r);
            printf("%d\n",query(l,r,(r-l+2)/2,0,1));
        }
    }
    return 0;
}