BST 80pts求助

#include <bits/stdc++.h>
#define int long long
#define inf LONG_LONG_MAX
using namespace std;
const int maxn = 100005;
struct treenode {
    int val, lc, rc, cnt, siz;
} tree[maxn];
int tsiz;

void insert(int x, int u) {
    tree[u].siz++;

    if (tree[u].val == x)
        tree[u].cnt++;

    if (tree[u].val < x) {
        if (tree[u].rc) {
            insert(x, tree[u].rc);
        } else {
            tree[++tsiz].val = x;
            tree[u].rc = tsiz;
            tree[tsiz].cnt = tree[tsiz].siz = 1;
        }
    } else {
        if (tree[u].lc) {
            insert(x, tree[u].lc);
        } else {
            tree[++tsiz].val = x;
            tree[u].lc = tsiz;
            tree[tsiz].cnt = tree[tsiz].siz = 1;
        }
    }
}

inline int qv(int rk, int u) {
    if (!u)
        return 0;

    if (rk == 0)
        return 0;

    if (tree[tree[u].lc].siz >= rk) {
        return qv(rk, tree[u].lc);
    } else if (tree[tree[u].lc].siz + tree[u].cnt >= rk) {
        return tree[u].val;
    } else {
        return qv(rk - tree[tree[u].lc].siz - tree[u].cnt, tree[u].rc);
    }
}

signed main() {
    int n; cin >> n;
    for (int i = 1; i <= n; ++i) {
        int x; cin >> x;
        if (!tsiz) {
            tree[++tsiz].val = x;
            tree[tsiz].cnt = tree[tsiz].cnt = 1;
        } else {
            insert(x, 1);
        }
        if (i % 2) {
            cout << qv(i / 2 + 1, 1) << endl;
        }
    }
    return 0;
}

rt