洛谷P3369 【模板】普通平衡树 FHQ Treap

题目链接：https://www.luogu.com.cn/problem/P3369

FHQ Treap

示例程序：

#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5 + 5;
mt19937 rng(time(0));

struct Node {
	int ls, rs, key, pri, sz;
	Node() {}
	Node(int _key) { ls = rs = 0; key = _key; pri = rng(); sz = 1; }
} tr[maxn];
int rt, idx;

void push_up(int u) {
	int ls = tr[u].ls, rs = tr[u].rs;
	tr[u].sz = tr[ls].sz + tr[rs].sz + 1;
}

void split(int u, int x, int &L, int &R) {
	if (!u) {
		L = R = 0;
		return;
	}
	if (tr[u].key <= x) {
		L = u;
		split(tr[u].rs, x, tr[u].rs, R);
	}
	else {
		R = u;
		split(tr[u].ls, x, L, tr[u].ls);
	}
	push_up(u);
}

int merge(int L, int R) {
	if (!L || !R) return L + R;
	if (tr[L].pri > tr[R].pri) {
		tr[L].rs = merge(tr[L].rs, R);
		push_up(L);
		return L;
	}
	else {
		tr[R].ls = merge(L, tr[R].ls);
		push_up(R);
		return R;
	}
}

void ins(int x) {
	int L, R;
	split(rt, x, L, R);
	tr[++idx] = Node(x);
	rt = merge(merge(L, idx), R);
}

void del(int x) {
	int L, R, p;
	split(rt, x, L, R);
	split(L, x-1, L, p);
	p = merge(tr[p].ls, tr[p].rs);
	rt = merge(merge(L, p), R);
}

int rnk(int x) {
	int L, R;
	split(rt, x-1, L, R);
	int rk = tr[L].sz + 1;
	rt = merge(L, R);
	return rk;
}

int kth(int u, int k) {
	while (u) {
		int sz = tr[tr[u].ls].sz;
		if (sz + 1 == k)
			return u;
		else if (sz >= k)
			u = tr[u].ls;
		else 
			k -= sz + 1,
			u = tr[u].rs;
	}
	assert(1 == 0);
	return -1; // 不会到这一行 
}

int pre(int x) {
	int L, R;
	split(rt, x-1, L, R);
	int res = kth(L, tr[L].sz);
	rt = merge(L, R);
	return res;
}

int nxt(int x) {
	int L, R;
	split(rt, x, L, R);
	int res = kth(R, 1);
	rt = merge(L, R);
	return res;
}

int n, op, x;

int main() {
	scanf("%d", &n);
	while (n--) {
		scanf("%d%d", &op, &x);
		if (op == 1)
			ins(x);
		else if (op == 2)
			del(x);
		else if (op == 3)
			printf("%d\n", rnk(x));
		else if (op == 4)
			printf("%d\n", tr[ kth(rt, x) ].key);
		else if (op == 5)
			printf("%d\n", tr[ pre(x) ].key);
		else if (op == 6)
			printf("%d\n", tr[ nxt(x) ].key);
	}
	return 0;
}