rt，求助

#include <bits/stdc++.h>

#define debug(x) (cout << #x << " " << x << "\n")

using namespace std;

using ll = long long;

const int N = 1e5 + 5;

int n, tot, val[N], dat[N], cnt[N], sz[N], ch[N][2], root;

int New(int v) {
    val[++ tot] = v;
    dat[tot] = rand();
    cnt[tot] = sz[tot] = 1;
    return tot;
}

void pushup(int cur) { sz[cur] = sz[ch[cur][0]] + sz[ch[cur][1]] + cnt[cur]; }

void build() {
    root = New(-1e9), ch[root][1] = New(1e9);
    pushup(root);
}

void split(int cur, int v, int &x, int &y) {
    if (!cur) { x = y = 0; return ; }
    if (val[cur] <= v) {
        x = cur, split(ch[cur][1], v, ch[cur][1], y);
    } else {
        y = cur, split(ch[cur][0], v, x, ch[cur][0]);
    }
}

int merge(int x, int y) {
    if (!x || !y) return x + y;
    if (dat[x] < dat[y]) {
        ch[x][1] = merge(ch[x][1], y);
        pushup(x);
        return x;
    } else {
        ch[y][0] = merge(y, ch[y][0]);
        pushup(y);
        return y;     
    }
}

void insert(int v) {
    int x, y;
    split(root, v, x, y);
    int z = New(v);
    root = merge(merge(x, z), y);
}

void del(int v) {
    int x, y, z;
    split(root, v, x, z);
    split(root, v - 1, x, y);
    y = merge(ch[y][0], ch[y][1]);
    root = merge(merge(x, y), z);
}

int rnk(int v) {
    int x, y;
    split(root, v - 1, x, y);
    int ans = sz[x] + 1;
    root = merge(x, y);
    return ans;
}

int kth(int cur, int k) {
    int lsz = sz[ch[cur][0]];
    if (k == lsz + 1) return val[cur];
    if (k <= lsz) return kth(ch[cur][0], k);
    return kth(ch[cur][1], k - lsz - 1);
}

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    cin >> n;
    build();
    while (n --) {
        int opt, x; cin >> opt >> x;
        if (opt == 1) insert(x);
        else if (opt == 2) del(x);
        else if (opt == 3) cout << rnk(x) - 1 << "\n";
        else if (opt == 4) cout << kth(root, x + 1) << "\n";
        else if (opt == 5) cout << kth(root, rnk(x) - 1) << "\n";
        else if (opt == 6) cout << kth(root, rnk(x + 1)) << "\n";
    }
    return 0;
}