求动区间第k小（离线，线段树）

#include<bits/stdc++.h>
const int M = 1e5 + 10 ;
int n , m ;
int ql , qr , k ;
int a[M] , sum [M] , p[M] ;
int id = 0 ;

void build (int o , int l , int r)
{
    if (l == r) {
        sum[o] = 1 ;
        return ;
    }
    int mid = (l + r) >> 1 ;
    build (o << 1 , l , mid) ;
    build (o << 1 | 1 , mid + 1 , r ) ;
    sum[o] = sum[o << 1] + sum[o << 1 | 1] ;
}

void query (int o , int l , int r )
{
    if (id != -1) return ;
    if (l >= ql && r <= qr) {
        if (k > sum[o]) {
            k -= sum[o] ; return ;
        }
        if (l == r ) {  
            id = l ; return ;
        }
    }
    int mid = (l + r) >> 1 ;
    if (ql <= mid) query (o << 1 , l , mid ) ;
    if (qr > mid ) query (o << 1 | 1 , mid + 1 , r) ;
}

int main ()
{
    freopen ("a.txt" , "r" , stdin ) ;
    scanf ("%d%d" , &n , &m) ;
    for (int i = 1 ; i <= n ; i ++) {
        scanf ("%d" , &a[i]) ;
        p[i] = i ;
    }
    build (1 , 1 , n ) ;
    std::sort (p + 1 , p + 1 + n , [](int i , int j) {return a[i] <= a[j] ;}) ;
    while (m --) {
        id = -1 ;
        scanf ("%d%d%d" , &ql , &qr , &k) ;
        query (1 , 1 , n ) ;
        printf ("%d\n" , a[ p[id] ]) ;
    }
    return 0 ;
}