【主席树_模板题】POJ 2104 K-th Number

 POJ 2104 K-th Number

#include <iostream>
#include <cstdio>
#include <cmath>
#include <string>
#include <cstring>
#include <algorithm>
#include <limits>
#include <vector>
#include <stack>
#include <queue>
#include <set>
#include <map>
#define INF 0x3f3f3f3f
#define lowbit(x) x & (-x)

#define MID (l + r ) >> 1
#define lsn rt << 1
#define rsn rt << 1 | 1
#define Lson lsn, l, mid
#define Rson rsn, mid + 1, r
#define QL Lson, ql, qr
#define QR Rson, ql, qr
#define eps  1e-6

using namespace std;
typedef long long ll;
typedef unsigned long long ull;
const int maxN = 1e5 + 5;
int n, m;
vector<int>vt, disc;
int root[maxN], tot;
struct node{
    int ls, rs, num;
    node(int a = 0, int b = 0, int c = 0): ls(a), rs(b), num(c) {}
}tree[maxN * 20];
void update(int &now, int pre, int l, int r, int k)
{
    now = ++ tot;
    tree[now].ls = tree[pre].ls;
    tree[now].rs = tree[pre].rs;
    tree[now].num = tree[pre].num + 1;
    if(l == r) return;
    int mid = MID;
    if(k <= mid) update(tree[now].ls, tree[pre].ls, l, mid, k);
    else update(tree[now].rs, tree[pre].rs, mid + 1, r, k);
}
int query(int i, int j, int l, int r, int k)
{
    int dif = tree[tree[j].ls].num - tree[tree[i].ls].num;
    int mid = MID;
    if(l == r) return l;
    if(dif >= k) return query(tree[i].ls, tree[j].ls, l, mid, k);
    else return query(tree[i].rs, tree[j].rs, mid + 1, r, k - dif);
}
int main()
{
    scanf("%d%d", &n, &m);
    for(int i = 0; i < n; i ++ )
    {
        int a; scanf("%d", &a);
        vt.push_back(a); disc.push_back(a);
    }
    sort(disc.begin(), disc.end());
    disc.erase(unique(disc.begin(), disc.end()), disc.end());
    int UP = disc.size();
    for(int i = 1; i <= n; i ++ )
    {
        int th = lower_bound(disc.begin(), disc.end(), vt[i - 1]) - disc.begin() + 1;
        update(root[i], root[i - 1], 1, UP, th);
    }
    while(m -- )
    {
        int l, r, k; scanf("%d%d%d", &l, &r, &k);
        printf("%d\n", disc[query(root[l - 1], root[r], 1, UP, k) - 1]);
    }
    return 0;
}