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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/lca_jump.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); } LCAJump<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/lca_jump.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 3 "tree/lca_jump.hpp" // Source: https://codeforces.com/blog/entry/74847 template <typename GraphType, typename EdgeType> struct LCAJump { EdgeType E; vector<int> dep, par, jmp; void init(int N, GraphType &g, int rt) { dep.assign(N+1, 0); par.assign(N+1, -1); jmp.assign(N+1, -1); function<void(int, int)> dfs = [&] (int c, int p) { par[c] = p; if (c != rt) { if (dep[p] - dep[jmp[p]] == dep[jmp[p]] - dep[jmp[jmp[p]]]) jmp[c] = jmp[jmp[p]]; else jmp[c] = p; } for (auto to : g[c]) { int v = E.v(to); if (v != p) { dep[v] = dep[c] + 1; dfs(v, c); } } }; jmp[rt] = rt; dfs(rt, -1); } int findFirst(int u, function<bool(int)> check) { while (!check(u)) { if (!check(jmp[u])) u = jmp[u]; else u = par[u]; } return u; } int up(int u, int want) { while (dep[u] > want) { if (dep[jmp[u]] >= want) u = jmp[u]; else u = par[u]; } return u; } int lca(int a, int b) { if (dep[a] > dep[b]) swap(a, b); b = up(b, dep[a]); while (a != b) { if (jmp[a] != jmp[b]) { a = jmp[a]; b = jmp[b]; } else { a = par[a]; b = par[b]; } } return a; } }; #line 6 "tests/tree/lca_jump.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); } LCAJump<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); } }