verify/library_checker_lca.cpp

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Last update: 2026-05-30 18:08:28+09:00
Problem: https://judge.yosupo.jp/problem/lca

Depends on

Code

// competitive-verifier: PROBLEM https://judge.yosupo.jp/problem/lca

#include <bits/stdc++.h>
using namespace std;

#include "tree/lca.hpp"

#include "templates/alias.hpp"
#include "templates/macro.hpp"

int main() {
  ll N, Q;
  in(N, Q);
  vvi G(N);

  vi P(N - 1);
  in(P);

  rep(i, N - 1) G[P[i]].emplace_back(i + 1);

  LcaWithDoubling<ll> LCA(G);

  while (Q--) {
    ll u, v;
    in(u, v);

    out(LCA.lca(u, v));
  }
}

#line 1 "verify/library_checker_lca.cpp"
// competitive-verifier: PROBLEM https://judge.yosupo.jp/problem/lca

#include <bits/stdc++.h>
using namespace std;

#line 2 "tree/lca.hpp"

#line 4 "tree/lca.hpp"

#line 7 "templates/alias.hpp"

template <class T> using VC = std::vector<T>;
template <class T>
using rpriority_queue = std::priority_queue<T, VC<T>, std::greater<T>>;
using ll = long long;
using ld = long double;
using pii = std::pair<ll, ll>;
using vi = VC<ll>;
using vvi = VC<vi>;
using vvvi = VC<vvi>;
using vb = VC<bool>;
using vvb = VC<vb>;
using vf = VC<double>;
using vvf = VC<vf>;
using vpii = VC<pii>;
using vvpii = VC<vpii>;
using si = std::set<ll>;
using spii = std::set<pii>;
using mii = std::map<ll, ll>;
const std::string upperlist = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
const std::string lowerlist = "abcdefghijklmnopqrstuvwxyz";
#define mp make_pair
#define dms << " " <<

constexpr int MOD998 = 998244353;
#line 4 "templates/macro.hpp"

// 引数の長さで内容が変わるrep 参考: https://trap.jp/post/1224
#define overload4(a, b, c, d, ...) d
#define _rep(i, n) for (int i = 0; i < (int)(n); i++)
#define REP(i, a, b) for (int i = (int)(a); i < (int)(b); ++i)
#define rep(...) overload4(__VA_ARGS__, REP, _rep)(__VA_ARGS__)
#define _rrep(i, n) for (int i = n - 1; i >= 0; i--)
#define RREP(i, a, b) for (int i = (int)(b - 1); i >= (int)(a); i--)
#define rrep(...) overload4(__VA_ARGS__, RREP, _rrep)(__VA_ARGS__)

#define all(a) (a).begin(), (a).end()

template <typename T> bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T> bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

template <typename T1, typename T2>
std::istream &operator>>(std::istream &is, std::pair<T1, T2> &p) {
  is >> p.first >> p.second;
  return is;
}

template <typename T>
std::istream &operator>>(std::istream &is, std::vector<T> &v) {
  for (T &in : v)
    is >> in;
  return is;
}

template <typename T>
std::ostream &operator<<(std::ostream &os, const std::vector<T> &v) {
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    os << v[i] << (i + 1 == v.size() ? "" : " ");
  }
  return os;
}

// pythonのprintライクな関数 参考:
// https://nyaannyaan.github.io/library/template/inout.hpp
inline void out() { std::cout << std::endl; }
template <typename T, typename... U, char sep = ' '>
void out(const T &t, const U &...u) {
  std::cout << t;

  if (sizeof...(u))
    std::cout << sep;

  out(u...);
}

// cinの短縮関数 参考: https://nyaannyaan.github.io/library/template/inout.hpp
inline void in() {}
template <typename T, class... U> void in(T &t, U &...u) {
  std::cin >> t;
  in(u...);
}

template <typename T> inline T ceil_div(T a, T b) { return (a + b - 1) / b; }
template <typename T> inline T mod_pow(T a, T n, T mod) {
  T res = 1;
  while (n) {
    if (n % 2 != 0) {
      res *= a;
      res %= mod;
    }

    a *= a;
    a %= mod;

    n >>= 1;
  }

  return res;
}
template <typename T> inline T minus_mod(T a, T b) { return ((a % b) + b) % b; }

template <typename T> void apply_vec(std::vector<T> &v, T (*fn)(T)) {
  for (int i = 0; i < v.size(); i++)
    v[i] = fn(v[i]);
}
#line 7 "tree/lca.hpp"

template <std::integral T> struct LcaWithDoubling {
  VC<VC<T>> G, P;
  VC<T> D;
  T N, K;

  LcaWithDoubling(VC<VC<T>> G, T st = 0) : G{G}, N{static_cast<int>(G.size())} {
    assert(N > 0);
    assert(st < N);

    K = std::bit_width((unsigned)N);
    P.resize(K, VC<T>(N, -1));
    D.resize(N);

    auto dfs = [&](const auto &self, T cur, T par, T d) -> void {
      P[0][cur] = par;
      D[cur] = d;

      for (auto nxt : G[cur]) {
        if (nxt == par)
          continue;

        self(self, nxt, cur, d + 1);
      }
    };

    dfs(dfs, st, st, 0);

    rep(b, K - 1) rep(i, N) P[b + 1][i] = P[b][P[b][i]];
  }

  T lca(T u, T v) {
    if (D[u] < D[v])
      std::swap(u, v);

    rep(k, K) {
      if ((D[u] - D[v]) >> k & 1) {
        u = P[k][u];
      }
    }

    if (u == v) {
      return u;
    }

    rrep(k, K) {
      if (P[k][u] != P[k][v]) {
        u = P[k][u], v = P[k][v];
      }
    }

    return P[0][u];
  }
};
#line 7 "verify/library_checker_lca.cpp"

#line 10 "verify/library_checker_lca.cpp"

int main() {
  ll N, Q;
  in(N, Q);
  vvi G(N);

  vi P(N - 1);
  in(P);

  rep(i, N - 1) G[P[i]].emplace_back(i + 1);

  LcaWithDoubling<ll> LCA(G);

  while (Q--) {
    ll u, v;
    in(u, v);

    out(LCA.lca(u, v));
  }
}

Test cases

Env	Name	Status	Elapsed	Memory
g++	almost_line_00	AC	1613 ms	160 MB
g++	almost_line_01	AC	1848 ms	160 MB
g++	binary_00	AC	1080 ms	144 MB
g++	binary_01	AC	1073 ms	144 MB
g++	binary_02	AC	1233 ms	144 MB
g++	example_00	AC	2 ms	4 MB
g++	line_00	AC	1118 ms	145 MB
g++	line_01	AC	1123 ms	172 MB
g++	line_02	AC	695 ms	21 MB
g++	line_03	AC	251 ms	160 MB
g++	line_04	AC	336 ms	104 MB
g++	max_line_00	AC	1329 ms	185 MB
g++	max_line_01	AC	1831 ms	185 MB
g++	max_line_02	AC	1302 ms	185 MB
g++	max_random_00	AC	1159 ms	147 MB
g++	max_random_01	AC	1078 ms	147 MB
g++	max_random_02	AC	1446 ms	147 MB
g++	path_graph_root_centroid_00	AC	1616 ms	176 MB
g++	path_graph_root_centroid_01	AC	1585 ms	176 MB
g++	path_graph_root_centroid_02	AC	1585 ms	176 MB
g++	random_00	AC	881 ms	115 MB
g++	random_01	AC	1081 ms	136 MB
g++	random_02	AC	810 ms	17 MB
g++	random_03	AC	254 ms	126 MB
g++	random_04	AC	298 ms	83 MB