#include using namespace std; using lint = long long; using pi = array; #define sz(v) ((int)(v).size()) #define all(v) (v).begin(), (v).end() // Source: https://github.com/ecnerwala/cp-book/blob/master/src/top_tree.hpp /** * Top tree! * * Usage: * Make a `struct T : public top_tree_node_base` (CRTP), which implements * void update() * void downdate() * void do_flip_path() * void do_other_operation() ... * When update() is called, you can assume downdate() has already been called. * * In general, do_op() should eagerly apply the operation but not touch the * children. In downdate(), you can push down to the children with ch->do_op(). * WARNING: if different operations do not trivially commute, you *must* * implement a way to swap/alter them to compose in a consistent order, and you * must use that order when implementing downdate(). This can be nontrivial! * * Creating vertices: * n->is_path = n->is_vert = true; * n->update(); * * Creating edges: no setup/update() needed, just call * link(e, va, vb); * * Updates: * auto cur = get_path(va, vb); // or get_subtree(va, vb) * cur->do_stuff(); * cur->downdate(); * cur->update_all(); * * Node types: * path edges: compress(c[0], self, c[1]) * assert(is_path && !is_vert); * assert(c[0] && c[1]); * assert(c[0]->is_path && c[1]->is_path); * assert(!c[2]); * (path) vertices: self + rake(c[0], c[1]) * assert(is_path && is_vert); * assert(!c[2]); * if (c[0]) assert(!c[0]->is_path); * if (c[1]) assert(!c[1]->is_path); * non-path edges: rake(c[0], self + c[2], c[1]) * assert(!is_path && !is_vert); * assert(c[2]) * assert(c[2]->is_path); * if (c[0]) assert(!c[0]->is_path); * if (c[1]) assert(!c[1]->is_path); */ template struct top_tree_node_base { private: top_tree_node *derived_this() { return static_cast(this); } const top_tree_node *derived_this() const { return static_cast(this); } public: mutable top_tree_node *p = nullptr; std::array c{nullptr, nullptr, nullptr}; int d() const { assert(p); if (this == p->c[0]) { return 0; } else if (this == p->c[1]) { return 1; } else if (this == p->c[2]) { return 2; } else assert(false); } top_tree_node *&p_c() const { return p->c[d()]; } // p->c which points to you // 3 types of verts: path edges, path verts, non-path edges bool is_path; bool is_vert; bool r() const { return !p || p->is_path != is_path; } private: // Convenience wrappers for the derived functions. void do_flip_path() { derived_this()->do_flip_path(); } void downdate() { derived_this()->downdate(); } void update() { derived_this()->update(); } public: void downdate_all() { if (p) p->downdate_all(); downdate(); } // Returns the root top_tree_node *update_all() { top_tree_node *cur = derived_this(); cur->update(); while (cur->p) { cur = cur->p; cur->update(); } return cur; } private: void rot() { assert(!is_vert); assert(!r()); top_tree_node *pa = p; int x = d(); assert(x == 0 || x == 1); top_tree_node *ch = c[!x]; if (pa->p) pa->p_c() = derived_this(); this->p = pa->p; pa->c[x] = ch; if (ch) ch->p = pa; this->c[!x] = pa; pa->p = derived_this(); pa->update(); } void rot_2(int c_d) { assert(!is_vert); assert(!r()); assert(c[c_d]); assert(!c[c_d]->is_vert); if (d() == c_d) { rot(); return; } top_tree_node *pa = p; int x = d(); assert(x == 0 || x == 1); assert(c_d == !x); top_tree_node *ch = c[c_d]->c[!x]; if (pa->p) pa->p_c() = derived_this(); this->p = pa->p; pa->c[x] = ch; if (ch) ch->p = pa; this->c[c_d]->c[!x] = pa; pa->p = this->c[c_d]; pa->update(); } void splay_dir(int x) { while (!r() && d() == x) { if (!p->r() && p->d() == x) { p->rot(); } rot(); } } void splay_2(int c_d) { assert(!is_vert && is_path); assert(c[c_d] && !c[c_d]->is_vert); while (!r()) { if (!p->r()) { if (p->d() == d()) { p->rot(); } else { rot_2(c_d); } } rot_2(c_d); } } void splay_2() { assert(!is_vert && is_path); assert(!r()); p->splay_2(d()); } void splay_vert() { assert(is_vert); if (r()) { return; } p->splay_dir(d()); if (p->r()) { return; } assert(p->d() != d()); // we have a preference to be the left child if (d() == 1) { p->rot(); } assert(d() == 0); p->splay_2(); assert(d() == 0); assert(p->d() == 1); assert(p->p->r()); } void splay() { assert(!is_vert); while (!r()) { if (!p->r()) { if (p->d() == d()) { p->rot(); } else { rot(); } } rot(); } } top_tree_node *cut_right() { assert(is_vert && is_path); splay_vert(); if (r() || d() == 1) { assert(r() || (d() == 1 && p->r())); assert(c[0] == nullptr); return nullptr; } top_tree_node *pa = p; assert(pa->r() || (pa->d() == 1 && pa->p->r())); assert(!pa->is_vert); assert(pa->is_path); assert(pa->c[0] == this); assert(pa->c[2] == nullptr); if (pa->p) pa->p_c() = derived_this(); this->p = pa->p; pa->is_path = false; pa->c[2] = pa->c[1]; // don't need to change the parent pa->c[0] = c[0]; if (c[0]) c[0]->p = pa; pa->c[1] = c[1]; if (c[1]) c[1]->p = pa; c[0] = nullptr; c[1] = pa; pa->p = derived_this(); assert(c[2] == nullptr); assert(c[0] == nullptr); pa->update(); return pa; } top_tree_node *splice_non_path() { assert(!is_path); assert(!is_vert); splay(); assert(p && p->is_vert && p->is_path); p->cut_right(); if (!p->is_path) rot(); assert(p && p->is_vert && p->is_path); assert(p->r() || (p->d() == 1 && p->p->r())); assert(p->c[d()] == this && p->c[!d()] == nullptr); top_tree_node *pa = p; if (pa->p) pa->p_c() = derived_this(); this->p = pa->p; pa->c[0] = c[0]; if (c[0]) c[0]->p = pa; pa->c[1] = c[1]; if (c[1]) c[1]->p = pa; assert(c[2] && c[2]->is_path); c[1] = c[2]; // don't need to change parent c[0] = pa; pa->p = derived_this(); c[2] = nullptr; is_path = true; pa->update(); return pa; } // Return the topmost vertex which was spliced into top_tree_node *splice_all() { top_tree_node *res = nullptr; for (top_tree_node *cur = derived_this(); cur; cur = cur->p) { if (!cur->is_path) { res = cur->splice_non_path(); } assert(cur->is_path); } return res; } public: // Return the topmost vertex which was spliced into top_tree_node *expose() { assert(is_vert); downdate_all(); top_tree_node *res = splice_all(); cut_right(); update_all(); return res; } // Return the topmost vertex which was spliced into top_tree_node *expose_edge() { assert(!is_vert); downdate_all(); top_tree_node *v = is_path ? c[1] : c[2]; v->downdate(); while (!v->is_vert) { v = v->c[0]; v->downdate(); } top_tree_node *res = v->splice_all(); v->cut_right(); v->update_all(); assert(!p); assert(v == c[1]); return res; } // Return the new root top_tree_node *meld_path_end() { assert(!p); top_tree_node *rt = derived_this(); while (true) { rt->downdate(); if (rt->is_vert) break; rt = rt->c[1]; } assert(rt->is_vert); rt->splay_vert(); if (rt->c[0] && rt->c[1]) { top_tree_node *ch = rt->c[1]; while (true) { ch->downdate(); if (!ch->c[0]) break; ch = ch->c[0]; } ch->splay(); assert(ch->c[0] == nullptr); ch->c[0] = rt->c[0]; ch->c[0]->p = ch; rt->c[0] = nullptr; ch->update(); } else if (rt->c[0]) { rt->c[1] = rt->c[0]; rt->c[0] = nullptr; } assert(rt->c[0] == nullptr); return rt->update_all(); } void make_root() { expose(); top_tree_node *rt = derived_this(); while (rt->p) { assert(rt->d() == 1); rt = rt->p; } rt->do_flip_path(); rt->meld_path_end(); expose(); assert(!p); } // Link v2 as a child of v1 with edge e friend void link(top_tree_node *e, top_tree_node *v1, top_tree_node *v2) { assert(e && v1 && v2); assert(!e->c[0] && !e->c[1] && !e->c[2]); v1->expose(); while (v1->p) v1 = v1->p; v2->make_root(); assert(!v1->p); assert(!v2->p); e->is_path = true, e->is_vert = false; e->c[0] = v1; v1->p = e; e->c[1] = v2; v2->p = e; e->update(); } // Link v2's root as a child of v1 with edge e // Returns false if they're already in the same subtree friend bool link_root(top_tree_node *e, top_tree_node *v1, top_tree_node *v2) { assert(e && v1 && v2); assert(!e->c[0] && !e->c[1] && !e->c[2]); v1->expose(); v2->expose(); while (v1->p) v1 = v1->p; while (v2->p) v2 = v2->p; if (v1 == v2) return false; assert(!v1->p); assert(!v2->p); e->is_path = true, e->is_vert = false; e->c[0] = v1; v1->p = e; e->c[1] = v2; v2->p = e; e->update(); return true; } // Cuts the edge e // Returns the top-tree-root of the two halves; they are not necessarily the split vertices. friend std::pair cut(top_tree_node *e) { assert(!e->is_vert); e->expose_edge(); assert(!e->p); assert(e->is_path); top_tree_node *l = e->c[0]; top_tree_node *r = e->c[1]; assert(l && r); e->c[0] = e->c[1] = nullptr; l->p = r->p = nullptr; assert(e->c[2] == nullptr); l = l->meld_path_end(); return {l, r}; } friend top_tree_node *get_path(top_tree_node *a, top_tree_node *b) { assert(a->is_vert && b->is_vert); a->make_root(); b->expose(); if (a == b) { assert(!b->p); return b; } assert(!b->p->p); return b->p; } friend top_tree_node *get_subtree(top_tree_node *rt, top_tree_node *n) { rt->make_root(); n->expose(); return n; } }; struct node : public top_tree_node_base { bool lazy_flip_path = false; int vidx; int ends[2] = {}; // border index int endTails[2] = {}; // tails of each borders int proj[2] = {}; // projection end of max path int eventualReach[2] = {}; // where the max path ends? void do_flip_path() { assert(is_path); std::swap(c[0], c[1]); swap(ends[0], ends[1]); swap(endTails[0], endTails[1]); swap(proj[0], proj[1]); swap(eventualReach[0], eventualReach[1]); lazy_flip_path ^= 1; } void downdate() { if (lazy_flip_path) { assert(is_path); if (!is_vert) { c[0]->do_flip_path(); c[1]->do_flip_path(); } lazy_flip_path = false; } } // NOTE: You may assume downdate() has been called on the current node, but // it may not have been called on the children! In particular, be careful // when accessing grandchildren information. void update() { if (is_path) { if (is_vert) { ends[0] = ends[1] = vidx; proj[0] = proj[1] = vidx; int ta = -1, er = vidx; for (int i = 0; i < 2; i++) { if (c[i] && c[i]->proj[0] > ta) { ta = c[i]->proj[0]; er = c[i]->eventualReach[0]; } } endTails[0] = endTails[1] = ta; eventualReach[0] = eventualReach[1] = er; } else { ends[0] = c[0]->ends[0]; ends[1] = c[1]->ends[1]; endTails[0] = c[0]->endTails[0]; endTails[1] = c[1]->endTails[1]; if (c[0]->proj[0] == c[0]->ends[1] && c[0]->endTails[1] < c[1]->ends[0]) { proj[0] = c[1]->proj[0]; eventualReach[0] = c[1]->eventualReach[0]; } else { proj[0] = c[0]->proj[0]; eventualReach[0] = c[0]->eventualReach[0]; } if (c[1]->proj[1] == c[1]->ends[0] && c[1]->endTails[0] < c[0]->ends[1]) { proj[1] = c[0]->proj[1]; eventualReach[1] = c[0]->eventualReach[1]; } else { proj[1] = c[1]->proj[1]; eventualReach[1] = c[1]->eventualReach[1]; } } } else { proj[0] = c[2]->ends[0]; eventualReach[0] = c[2]->eventualReach[0]; // (proj, eventual reach) for (int i = 0; i < 2; i++) { if (c[i] && proj[0] < c[i]->proj[0]) { proj[0] = c[i]->proj[0]; eventualReach[0] = c[i]->eventualReach[0]; } } } } }; int main() { ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0); int n; cin >> n; vector ptr(n); vector a(n); vector rev(n); for (int i = 0; i < n; i++) { a[i] = rev[i] = i; ptr[i] = new node(); ptr[i]->vidx = i; ptr[i]->is_path = ptr[i]->is_vert = true; ptr[i]->update(); } for (int i = 0; i < n - 1; i++) { int u, v; cin >> u >> v; node *e = new node(); link(e, ptr[u - 1], ptr[v - 1]); } int q; cin >> q; int last = 0; while (q--) { int u, v; cin >> u >> v; u = (u + n - 1 + last) % n; v = (v + n - 1 + last) % n; swap(a[u], a[v]); swap(rev[a[u]], rev[a[v]]); ptr[v]->make_root(); ptr[v]->vidx = a[v]; ptr[v]->update_all(); ptr[u]->make_root(); ptr[u]->vidx = a[u]; ptr[u]->update_all(); cout << (last = (rev[ptr[u]->eventualReach[0]] + 1)) << "\n"; } }