AcWing2437. Splay 题解 FHQ Treap

题目链接：https://www.acwing.com/problem/content/2439/

解题思路：

翻转，加懒惰标记

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;
	bool flag;
	Node() {}
	Node(int _key) { ls = rs = 0; key = _key; pri = rng(); sz = 1; flag = false; }
} 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 push_down(int u) {
    if (tr[u].flag) {
        int ls = tr[u].ls, rs = tr[u].rs;
        if (ls) {
            tr[ls].flag ^= 1;
            swap(tr[ls].ls, tr[ls].rs);
        }
        if (rs) {
            tr[rs].flag ^= 1;
            swap(tr[rs].ls, tr[rs].rs);
        }
        tr[u].flag = false;
    }
}

void split(int u, int rk, int &L, int &R) {
	if (!u) {
		L = R = 0;
		return;
	}
	push_down(u);
	int ls = tr[u].ls;
	if (tr[ls].sz + 1 <= rk) {
		L = u;
		split(tr[u].rs, rk  - tr[ls].sz - 1, tr[u].rs, R);
	}
	else {
		R = u;
		split(tr[u].ls, rk, L, tr[u].ls);
	}
	push_up(u);
}

int merge(int L, int R) {
	if (!L || !R) return L + R;
	push_down(L);
	push_down(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;
	}
}

int build(int l, int r) {
    if (l > r) return 0;
    int u = ++idx;
    int mid = (l + r) / 2;
    tr[u] = Node(mid);
    tr[u].ls = build(l, mid-1);
    tr[u].rs = build(mid+1, r);
    push_up(u);
    return u;
}

void output(int u) {
    if (!u) return;
    push_down(u);
    output(tr[u].ls);
    printf("%d ", tr[u].key);
    output(tr[u].rs);
}

int n, m;

void rev(int l, int r) {
    int L, p, R;
    split(rt, l-1, L, R);
    split(R, r-l+1, p, R);
    assert(p);
    swap(tr[p].ls, tr[p].rs);
    tr[p].flag ^= 1;
    R = merge(p, R);
    rt = merge(L, R);
}

int main() {
    scanf("%d%d", &n, &m);
    rt = build(1, n);
    while (m--) {
        int l, r;
        scanf("%d%d", &l, &r);
        rev(l, r);
    }
    output(rt);
    return 0;
}