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#define PROBLEM "https://judge.yosupo.jp/problem/lca" #include "../../template.hpp" #include "../test_utils.hpp" #include "../../graph/edge_types.hpp" #include "../../tree/hld.hpp" const int MN = 5e5 + 1; vector<int> g[MN]; int main() { fast_io(); int N = readi(), Q = readi(); // Randomizer to make sure code does not fail on trees where par_i < i does not always hold mt19937 mt(26022021); vector<int> P(N+1), iP(N+1); iota(P.begin()+1, P.end(), 1); shuffle(P.begin()+1, P.end(), mt); for (int i = 1; i <= N; i++) iP[P[i]] = i; for (int i = 2; i <= N; i++) { int p = readi()+1, a = P[i], b = P[p]; g[a].push_back(b); g[b].push_back(a); } HLD<vector<int>[MN], Edge> lca; lca.init(N, g, P[1]); while (Q--) { int u = P[readi()+1]; int v = P[readi()+1]; print(iP[lca.lca(u, v)]-1); } }
#line 1 "tests/tree/hld_lca.test.cpp" #define PROBLEM "https://judge.yosupo.jp/problem/lca" #line 2 "template.hpp" #include <bits/stdc++.h> #define DEBUG 1 using namespace std; // Defines #define fs first #define sn second #define pb push_back #define eb emplace_back #define mpr make_pair #define mtp make_tuple #define all(x) (x).begin(), (x).end() // Basic type definitions #if __cplusplus == 201703L // CPP17 only things template <typename T> using opt_ref = optional<reference_wrapper<T>>; // for some templates #endif using ll = long long; using ull = unsigned long long; using ld = long double; using pii = pair<int, int>; using pll = pair<long long, long long>; #ifdef __GNUG__ // PBDS order statistic tree #include <ext/pb_ds/assoc_container.hpp> // Common file #include <ext/pb_ds/tree_policy.hpp> using namespace __gnu_pbds; template <typename T, class comp = less<T>> using os_tree = tree<T, null_type, comp, rb_tree_tag, tree_order_statistics_node_update>; template <typename K, typename V, class comp = less<K>> using treemap = tree<K, V, comp, rb_tree_tag, tree_order_statistics_node_update>; // HashSet #include <ext/pb_ds/assoc_container.hpp> template <typename T, class Hash> using hashset = gp_hash_table<T, null_type, Hash>; template <typename K, typename V, class Hash> using hashmap = gp_hash_table<K, V, Hash>; const ll RANDOM = chrono::high_resolution_clock::now().time_since_epoch().count(); struct chash { ll operator()(ll x) const { return x ^ RANDOM; } }; #endif // More utilities int SZ(string &v) { return v.length(); } template <typename C> int SZ(C &v) { return v.size(); } template <typename C> void UNIQUE(vector<C> &v) { sort(v.begin(), v.end()); v.resize(unique(v.begin(), v.end()) - v.begin()); } template <typename T, typename U> void maxa(T &a, U b) { a = max(a, b); } template <typename T, typename U> void mina(T &a, U b) { a = min(a, b); } const ll INF = 0x3f3f3f3f, LLINF = 0x3f3f3f3f3f3f3f3f; #line 3 "tests/test_utils.hpp" // I/O template <typename T> void print(T v) { cout << v << '\n'; } template <typename T, typename... Rest> void print(T v, Rest... vs) { cout << v << ' '; print(vs...); } void fast_io() { ios_base::sync_with_stdio(false); cin.tie(NULL); } // Reading operators template <typename T, typename U> istream& operator>>(istream& in, pair<T, U> &o) { return in >> o.first >> o.second; } // Read helpers int readi() { int x; cin >> x; return x; } ll readl() { ll x; cin >> x; return x; } template <typename T> vector<T> readv(int n) { vector<T> res(n); for (auto &x : res) cin >> x; return res; } // Functional stuff template <typename T> vector<pair<int, T>> enumerate(vector<T> v, int start = 0) { vector<pair<int, T>> res; for (auto &x : v) res.emplace_back(start++, x); return res; } #line 3 "graph/edge_types.hpp" struct Edge { using EdgeType = int; int v(EdgeType e) { return e; } int w(EdgeType e) { return 1; } int i(EdgeType e) { throw domain_error("no information on edge indices"); } EdgeType swapNode(EdgeType e, int v) { return v; } }; template <typename T> struct WeightedEdge { using EdgeType = pair<int, T>; using WeightType = T; int v(EdgeType e) { return e.first; } T w(EdgeType e) { return e.second; } int i(EdgeType e) { throw domain_error("no information on edge indices"); } EdgeType swapNode(EdgeType e, int v) { return {v, w(e)}; } }; struct IndexedEdge { using EdgeType = pair<int, int>; int v(EdgeType e) { return e.first; } int w(EdgeType e) { return 1; } int i(EdgeType e) { return e.second; } EdgeType swapNode(EdgeType e, int v) { return {v, i(e)}; } }; template <typename T> struct WeightedIndexedEdge { using EdgeType = tuple<int, T, int>; using WeightType = T; int v(EdgeType e) { return get<0>(e); } T w(EdgeType e) { return get<1>(e); } int i(EdgeType e) { return get<2>(e); } EdgeType swapNode(EdgeType e, int v) { return {v, w(e), i(e)}; } }; #line 1 "tree/hld.hpp" template <typename GraphType, typename EdgeType> struct HLD { EdgeType E; int cpos; vector<int> par, dep, head, heavy, pos; void init(int N, GraphType &g, int rt) { cpos = 0; par.assign(N + 1, 0); dep.assign(N + 1, 0); head.assign(N + 1, 0); heavy.assign(N + 1, -1); pos.assign(N + 1, 0); function<int(int, int)> dfs = [&] (int c, int p) { par[c] = p; int sz = 1, mxsz = 0; for (auto to : g[c]) { int v = E.v(to); if (v != p) { dep[v] = dep[c] + 1; int csz = dfs(v, c); sz += csz; if (csz > mxsz) heavy[c] = v, mxsz = csz; } } return sz; }; function<void(int, int)> build = [&] (int c, int chead) { pos[c] = ++cpos; head[c] = chead; if (heavy[c] != -1) build(heavy[c], chead); for (auto to : g[c]) { int v = E.v(to); if (v != par[c] && v != heavy[c]) build(v, v); } }; dfs(rt, -1); build(rt, rt); } int lca(int a, int b) { while (head[a] != head[b]) { if (dep[head[a]] > dep[head[b]]) swap(a, b); b = par[head[b]]; } return dep[a] < dep[b] ? a : b; } #if __cplusplus == 201703L // CPP17 only things void bind(opt_ref<vector<int>> par0, opt_ref<vector<int>> dep0, opt_ref<vector<int>> head0, opt_ref<vector<int>> heavy0, opt_ref<vector<int>> pos0) { if (par0) par.swap(*par0); if (dep0) dep.swap(*dep0); if (head0) head.swap(*head0); if (heavy0) heavy.swap(*heavy0); if (pos0) pos.swap(*pos0); } #endif }; #line 6 "tests/tree/hld_lca.test.cpp" const int MN = 5e5 + 1; vector<int> g[MN]; int main() { fast_io(); int N = readi(), Q = readi(); // Randomizer to make sure code does not fail on trees where par_i < i does not always hold mt19937 mt(26022021); vector<int> P(N+1), iP(N+1); iota(P.begin()+1, P.end(), 1); shuffle(P.begin()+1, P.end(), mt); for (int i = 1; i <= N; i++) iP[P[i]] = i; for (int i = 2; i <= N; i++) { int p = readi()+1, a = P[i], b = P[p]; g[a].push_back(b); g[b].push_back(a); } HLD<vector<int>[MN], Edge> lca; lca.init(N, g, P[1]); while (Q--) { int u = P[readi()+1]; int v = P[readi()+1]; print(iP[lca.lca(u, v)]-1); } }