划分树-模版（求区间第K大）

//复杂度log(n)

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <limits.h>
#include <malloc.h>
#include <ctype.h>
#include <math.h>
#include <string>
#include <iostream>
#include <algorithm>
#include <queue>
#include<cmath>
using namespace std;
#include <vector>

const int MAXN = 100010;
int tree[20][MAXN];//表示每层每个位置的值
int sorted[MAXN];//已经排序好的数
int toleft[20][MAXN];//toleft[p][i]表示第p层从1到i有数分入左边
void build(int l,int r,int dep)
{
    if(l == r)return;
    int mid = (l+r)>>1;
    int same = mid - l + 1;//表示等于中间值而且被分入左边的个数
    for(int i = l; i <= r; i++) //注意是l,不是one
    if(tree[dep][i] < sorted[mid])
    same--;
    int lpos = l;
    int rpos = mid+1;
    for(int i = l;i <= r;i++)
    {
        if(tree[dep][i] < sorted[mid])
        tree[dep+1][lpos++] = tree[dep][i];
        else if(tree[dep][i] == sorted[mid] && same > 0)
        {
            tree[dep+1][lpos++] = tree[dep][i];
            same--;
        }
        else
        tree[dep+1][rpos++] = tree[dep][i];
        toleft[dep][i] = toleft[dep][l-1] + lpos - l;
    }
    build(l,mid,dep+1);
    build(mid+1,r,dep+1);
}

//查询区间第k大的数,[L,R]是大区间，[l,r]是要查询的小区间
//query(1,n,s,t,0,k)::  s-t区间内第k大
int query(int L,int R,int l,int r,int dep,int k)
{
    if(l == r)return tree[dep][l];
    int mid = (L+R)>>1;
    int cnt = toleft[dep][r] - toleft[dep][l-1];
    if(cnt >= k)
    {
        int newl = L + toleft[dep][l-1] - toleft[dep][L-1];
        int newr = newl + cnt - 1;
        return query(L,mid,newl,newr,dep+1,k);
    }
    else
    {
        int newr = r + toleft[dep][R] - toleft[dep][r];
        int newl = newr - (r-l-cnt);
        return query(mid+1,R,newl,newr,dep+1,k-cnt);
    }
}


int main()
{
    int n,m;
    int T;
    scanf("%d",&T);
    while(T--)
    {
        scanf("%d%d",&n,&m);

//------------------------------build
        memset(tree,0,sizeof(tree));
        for(int i = 1;i <= n;i++)
        {
            scanf("%d",&tree[0][i]);
            sorted[i] = tree[0][i];
        }
        sort(sorted+1,sorted+n+1);
        build(1,n,0);
//------------------------------build


        int s,t,k;
        while(m--)
        {
            scanf("%d%d%d",&s,&t,&k);
            printf("%d
",query(1,n,s,t,0,k));
        }
    }
    return 0;
}