K-th Number

http://poj.org/problem?id=2104

https://blog.csdn.net/Daxian911/article/details/89075748

题目：

代码：

#include<iostream>
#include<stdio.h>
#include<algorithm>
using namespace std;
const int maxn = 1e5+6;
int a[maxn],b[maxn],root[maxn];
int n,q,tot=0;
struct node{
    int l,r;
    int val;
}e[maxn*22];

void build(int l,int r,int &cur){
    cur=++tot;
    e[cur].val = 0;
    if(l==r) return ;
    int mid = l+r>>1;
    build(l,mid,e[cur].l);
    build(mid+1,r,e[cur].r);
}
void update(int pre,int &cur,int l,int r,int pos){
    cur = ++tot;
    e[cur] = e[pre];
    e[cur].val++;
    if(l==r) return ;
    int mid = r+l>>1;
    if(pos<=mid)
        update(e[pre].l,e[cur].l,l,mid,pos);
    else
        update(e[pre].r,e[cur].r,mid+1,r,pos);
}

int query(int pre,int cur,int l,int r,int val){
    if(l==r)
        return l;
    int sum = e[e[cur].l].val -e[e[pre].l].val;
    int mid = l+r>>1;
    if(val<=sum)
        return query(e[pre].l,e[cur].l,l,mid,val);
    else
        return  query(e[pre].r,e[cur].r,mid+1,r,val-sum);
}
int main(){
    scanf("%d%d",&n,&q);
    for(int i=1;i<=n;i++){
        scanf("%d",&a[i]);
        b[i] = a[i];
    }
    sort(b+1,b+1+n);
    int len = unique(b+1,b+1+n)-(b+1);
    build(1,len,root[0]);
    for(int i=1;i<=n;i++){
        int x = lower_bound(b+1,b+len+1,a[i])-b;
        update(root[i-1],root[i],1,len,x);
    }
    while(q--){
        int l,r,val;
        scanf("%d%d%d",&l,&r,&val);
        printf("%d\n",b[query(root[l-1],root[r],1,len,val)]);
    }
    return 0;
}