AcWing2437. Splay 题解

题目大意：splay 执行区间翻转

示例程序：

#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5 + 5;

int n, m;
struct Node {
    int s[2], p, v;
    int sz, flag;

    Node() {};
    Node(int _v, int _p) {v = _v; p = _p; s[0] = s[1] = 0; flag = 0; sz = 1;}
} tr[maxn];
int root, idx;

void push_up(int x) {
    tr[x].sz = tr[tr[x].s[0]].sz + tr[tr[x].s[1]].sz + 1;
}

void t_swap(int x) {
    tr[x].flag ^= 1;
    swap(tr[x].s[0], tr[x].s[1]);
}

void push_down(int x) {
    if (tr[x].flag) {
        t_swap(tr[x].s[0]);
        t_swap(tr[x].s[1]);
        tr[x].flag = 0;
    }
}

void f_s(int p, int u, bool k) {
    tr[p].s[k] = u;
    tr[u].p = p;
}

void rot(int x) {
    int y = tr[x].p, z = tr[y].p;
    bool k = tr[y].s[1] == x;
    f_s(z, x, tr[z].s[1]==y);
    f_s(y, tr[x].s[k^1], k);
    f_s(x, y, k^1);
    push_up(y), push_up(x);
}

void splay(int x, int k) {
    while (tr[x].p != k) {
        int y = tr[x].p, z = tr[y].p;
        if (z != k)
            (tr[y].s[1]==x) ^ (tr[z].s[1]==y) ? rot(x) : rot(y);
        rot(x);
    }
    if (!k) root = x;
}

void ins(int v) {
    int u = root, p = 0;
    while (u) {
        p = u, u = tr[u].s[v > tr[u].v];
    }
    tr[u = ++idx] = Node(v, p);
    if (p) tr[p].s[v > tr[p].v] = u;
    splay(u, 0);
}

int get_k(int k) {
    int u = root;
    while (u) {
        push_down(u);
        if (tr[tr[u].s[0]].sz >= k) u = tr[u].s[0];
        else if (tr[tr[u].s[0]].sz + 1 == k) return u;
        else k -= tr[tr[u].s[0]].sz + 1, u = tr[u].s[1];
    }
    return -1;
}

void output(int u) {
    if (!u) return;
    push_down(u);
    output(tr[u].s[0]);
    if (tr[u].v >= 1 && tr[u].v <= n) printf("%d ", tr[u].v);
    output(tr[u].s[1]);
}

int main() {
    scanf("%d%d", &n, &m);
    for (int i = 0; i <= n+1; i++) {
        ins(i);
    }
    while (m--) {
        int l, r;
        scanf("%d%d", &l, &r);
        l = get_k(l), r = get_k(r+2);
        splay(l, 0), splay(r, l);
        t_swap(tr[r].s[0]);
    }
    output(root);
    return 0;
}