动态开点主席树

C++ 代码

#include <bits/stdc++.h>
using namespace std;

const int N = 1e5 + 10, inf = 1e9;
int n, m, a[N], root[N], idx;
struct Node {
    int l, r, cnt;
}tr[N << 5];

void insert(int &q, int p, int l, int r, int x) {
    q = ++ idx;
    tr[q] = tr[p];
    tr[q].cnt ++;
    if (l == r) return;
    int mid = l + r >> 1;
    if (x <= mid) insert(tr[q].l, tr[p].l, l, mid, x);
    else insert(tr[q].r, tr[p].r, mid + 1, r, x);
}

int query(int p, int q, int l, int r, int k) {
    if (l == r) return l;
    int cnt = tr[tr[q].l].cnt - tr[tr[p].l].cnt;
    int mid = l + r >> 1;
    if (cnt >= k) return query(tr[p].l, tr[q].l, l, mid, k);
    return query(tr[p].r, tr[q].r, mid + 1, r, k - cnt);
}

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    cin >> n >> m;
    for (int i = 1; i <= n; i ++ ) {
        cin >> a[i];
        insert(root[i], root[i - 1], -inf, inf, a[i]);
    }
    int l, r, k;
    for (int i = 0; i < m; i ++ ) {
        cin >> l >> r >> k;
        cout << query(root[l - 1], root[r], -inf, inf, k) << endl;
    }
    return 0;
}