题目链接
对于每一个节点，记录这个节点所在链的信息：
ls:（链的上端点）距离链内部近期的白点距离
rs:（链的下端点）距离链内部近期的白点距离
注意以上都是实边
虚边的信息用一个set维护。
set维护的是对于每一个不是链上，可是this的子树，那些子树中距离this近期的白点距离。

#include <stdio.h>
#include <string.h>
#include <set>
#include <algorithm>
#include <iostream>
#include <vector>
template <class T>
inline bool rd(T &ret) {char c; int sgn;if (c = getchar(), c == EOF) return 0;while (c != '-' && (c<'0' || c>'9')) c = getchar();sgn = (c == '-') ?

-1 : 1; ret = (c == '-') ? 0 : (c - '0'); while (c = getchar(), c >= '0'&&c <= '9') ret = ret * 10 + (c - '0'); ret *= sgn; return 1; } template <class T> inline void pt(T x) { if (x <0) { putchar('-'); x = -x; } if (x>9) pt(x / 10); putchar(x % 10 + '0'); } using namespace std; typedef long long ll; const int inf = 1e9; const int N = 1e5 + 10; struct Node *null; struct Node{ multiset<int>chain; Node *fa, *ch[2]; int size; int col, ls, rs, id, len, edge; //黑色col=-inf, 白色col=0 len是链长 bool rev; inline void put(){ printf("%d son:%d,%d fa:%d len:%d (%d,%d) col:%d\n", id, ch[0]->id, ch[1]->id, fa->id, len, ls, rs, col); for (auto i : chain)printf("%d ", i); puts(""); } inline void clear(int _id){ fa = ch[0] = ch[1] = null; size = 1; rev = 0; len = edge = 0; id = _id; chain.clear(); chain.insert(inf); col = inf; ls = rs = inf; } inline void push_up(){ size = 1 + ch[0]->size + ch[1]->size; len = edge + ch[0]->len + ch[1]->len; int m0 = min(col, *chain.begin()), ml = min(m0, ch[0]->rs + edge), mr = min(m0, ch[1]->ls); ls = min(ch[0]->ls, ch[0]->len + edge + mr); rs = min(ch[1]->rs, ch[1]->len + ml); } inline void push_down(){ if (rev){ ch[0]->flip(); ch[1]->flip(); rev = 0; } } inline void setc(Node *p, int d){ ch[d] = p; p->fa = this; } inline bool d(){ return fa->ch[1] == this; } inline bool isroot(){ return fa == null || fa->ch[0] != this && fa->ch[1] != this; } inline void flip(){ if (this == null)return; swap(ch[0], ch[1]); rev ^= 1; } inline void go(){//从链头開始更新到this if (!isroot())fa->go(); push_down(); } inline void rot(){ Node *f = fa, *ff = fa->fa; int c = d(), cc = fa->d(); f->setc(ch[!c], c); this->setc(f, !c); if (ff->ch[cc] == f)ff->setc(this, cc); else this->fa = ff; f->push_up(); } inline Node*splay(){ go(); while (!isroot()){ if (!fa->isroot()) d() == fa->d() ? fa->rot() : rot(); rot(); } push_up(); return this; } void debug(Node *x){ if (x == null)return; x->put(); debug(x->ch[0]); debug(x->ch[1]); } inline Node* access(){//access后this就是到根的一条splay，而且this已经是这个splay的根了 for (Node *p = this, *q = null; p != null; q = p, p = p->fa){ p->splay(); // debug(q); puts(""); debug(p); puts(""); if (p->ch[1] != null) p->chain.insert(p->ch[1]->ls); if (q != null) p->chain.erase(p->chain.find( q->ls )); p->setc(q, 1); p->push_up(); // debug(q); puts(""); debug(p); puts(""); } return splay(); } inline Node* find_root(){ Node *x; for (x = access(); x->push_down(), x->ch[0] != null; x = x->ch[0]); return x; } void make_root(){ access()->flip(); } void cut(){//把这个点的子树脱离出去 access(); ch[0]->fa = null; ch[0] = null; push_up(); } void cut(Node *x){ if (this == x || find_root() != x->find_root())return; else { x->make_root(); cut(); } } void link(Node *x){ if (find_root() == x->find_root())return; else { make_root(); fa = x; } } }; Node pool[N], *tail; Node *node[N]; vector<int>G[N]; void dfs(int u, int fa){ for (int v : G[u]){ if (v == fa)continue; node[v]->fa = node[u]; node[v]->edge = 1; dfs(v, u); node[u]->chain.insert(node[v]->ls); } node[u]->push_up(); } int n, q; void debug(Node *x){ if (x == null)return; x->put(); debug(x->ch[0]); debug(x->ch[1]); } int main(){ while (cin >> n){ tail = pool; null = tail++; null->clear(0); null->size = 0; for (int i = 1; i <= n; i++) { G[i].clear(); node[i] = tail++; node[i]->clear(i); } for (int i = 1, u, v; i < n; i++){ rd(u); rd(v); G[u].push_back(v); G[v].push_back(u); } dfs(1, 1); // for (int i = 1; i <= n; i++)debug(node[i]), puts(""); rd(q); while (q--){ int u, v; rd(u); rd(v); if (u == 0) { node[v]->access(); if (node[v]->col == inf)node[v]->col = 0; else node[v]->col = inf; node[v]->push_up(); } else { node[v]->access(); int ans = min(*node[v]->chain.begin(), node[v]->rs); if (ans == inf)ans = -1; pt(ans); puts(""); } // for (int i = 1; i <= n; i++)debug(node[i]), puts(""); } } return 0; }