HDU 2665 Kth number (主席树)

题目链接：https://vjudge.net/contest/313769#problem/A

#include <cmath>
#include <cstdio>
#include <algorithm>
#include <iostream>
#include <cstring>
#include <ctype.h>
#include <map>
#include <vector>
#include <set>
#include <bitset>
#define lson rt << 1, l, mid
#define rson rt << 1 | 1, mid + 1, r
using namespace std;
static const int MAX_N = 1e5 + 5;
vector<int>vec;
struct Node{
    int l, r, sum;
}T[MAX_N * 20];
int root[MAX_N], a[MAX_N], cnt, n;
int getId(int x){return lower_bound(vec.begin(), vec.end(), x) - vec.begin() + 1;}  //二分查找
void update(int l, int r, int &x, int y, int pos){
    T[++cnt] = T[y], T[cnt].sum++, x = cnt;
    if(l == r) return ;
    int mid = l + r >> 1;
    if(pos <= mid) update(l, mid, T[x].l, T[y].l, pos);
    else update(mid + 1, r, T[x].r, T[x].r, pos);
}
int query(int l, int r, int x, int y, int k){
    if(l == r) return l;
    int mid = l + r >> 1;
    int sum = T[T[y].l].sum - T[T[x].l].sum;
    if(sum >= k) return query(l, mid, T[x].l, T[y].l, k);
    else return query(mid + 1, r, T[x].r, T[y].r, k - sum);
}
void prework(){
    cnt = 0;
    vec.clear();
}
int main(){
//    freopen("input.txt", "r", stdin);
//    freopen("output.txt", "w", stdout);
    int t;
    scanf("%d", &t);
    while(t--){
        prework();
        int m;
        scanf("%d%d", &n, &m);
        for(int i = 1; i <= n; ++i) scanf("%d", &a[i]), vec.push_back(a[i]);
        sort(vec.begin(), vec.end()), vec.erase(unique(vec.begin(), vec.end()), vec.end());//离散化
        for(int i = 1; i <= n; ++i) update(1, n, root[i], root[i - 1], getId(a[i]));
        while(m--){
            int ql, qr, k;
            scanf("%d%d%d", &ql, &qr, &k);
            printf("%d\n", vec[query(1, n, root[ql - 1], root[qr], k) - 1]);
        }
    }
    return 0;
}