POJ 2104 K-th Number （主席树 || 划分树）

静态区间查询第K大   主席树入门  也可以用划分树

//#include <bits/stdc++.h>
#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
using namespace std;

const int MAXN = 100010;
const int M = MAXN * 30;
int n,q,m,tot;
int a[MAXN], t[MAXN];
int T[M], lson[M], rson[M], c[M];

void Init_Hash()
{
    for(int i = 1; i <= n; i++)
        t[i] = a[i];
    sort(t+1,t+1+n);
    m = unique(t+1,t+1+n)-t-1;  //去重
}

int build(int l,int r)
{
    int root = tot++;
    c[root] = 0;
    if(l != r)
    {
        int mid = (l+r)>>1;
        lson[root] = build(l,mid);
        rson[root] = build(mid+1,r);
    }
    return root;
}

int Hash(int x)
{
    return lower_bound(t+1,t+1+m,x) - t; //找中位数
}

int update(int root,int pos,int val)
{
    int newroot = tot++, tmp = newroot;
    c[newroot] = c[root] + val;
    int l = 1, r = m;
    while(l < r)
    {
        int mid = (l+r)>>1;
        if(pos <= mid)
        {
            lson[newroot] = tot++;
            rson[newroot] = rson[root];
            newroot = lson[newroot];
            root = lson[root];
            r = mid;
        }
        else
        {
            rson[newroot] = tot++;
            lson[newroot] = lson[root];
            newroot = rson[newroot];
            root = rson[root];
            l = mid+1;
        }
        c[newroot] = c[root] + val;
    }
    return tmp;
}

int query(int left_root,int right_root,int k)
{
    int l = 1, r = m;
    while( l < r)
    {
        int mid = (l+r)>>1;
        if(c[lson[left_root]]-c[lson[right_root]] >= k )
        {
            r = mid;
            left_root = lson[left_root];
            right_root = lson[right_root];
        }
        else
        {
            l = mid + 1;
            k -= c[lson[left_root]] - c[lson[right_root]];
            left_root = rson[left_root];
            right_root = rson[right_root];
        }
    }
    return l;
}

int main()
{
    while(scanf("%d%d",&n,&q) == 2)
    {
        tot = 0;
        for(int i = 1; i <= n; i++)
            scanf("%d",&a[i]);
        Init_Hash();                    //离散建树
        T[n+1] = build(1,m);
        for(int i = n; i ; i--)   
        {
            int pos = Hash(a[i]);
            T[i] = update(T[i+1],pos,1);
        }
        while(q--)
        {
            int l,r,k;
            scanf("%d%d%d",&l,&r,&k);
            printf("%d\n",t[query(T[l],T[r+1],k)]);
        }
    }
    return 0;
}
//#include <bit