Tifa's CP Library

:warning: centroid (src/code/tree/centroid.hpp)

Depends on

Code

#ifndef TIFALIBS_TREE_CENTROID
#define TIFALIBS_TREE_CENTROID

#include "tree.hpp"

namespace tifa_libs::graph {

// @return centroid, at MOST 2
constexpr vecu tree_centroid(tree const &tr) {
  vecu sz(tr.g.size()), ans;

  auto dfs = [&](auto &&dfs, u32 now, u32 fa = -1_u32) -> void {
    sz[now] = 1;
    u32 max_sz = 0;
    for (u32 to : tr.g[now])
      if (to != fa) {
        dfs(dfs, to, now);
        sz[now] += sz[to];
        max_sz = std::max(max_sz, sz[to]);
      }
    if (std::max(max_sz, (u32)tr.g.size() - sz[now]) <= tr.g.size() / 2) ans.push_back(now);
  };

  dfs(dfs, tr.root);
  return ans;
}

}  // namespace tifa_libs::graph

#endif
#line 1 "src/code/tree/centroid.hpp"



#line 1 "src/code/tree/tree.hpp"



#line 1 "src/code/graph/alist.hpp"



#line 1 "src/code/util/util.hpp"



#include <bits/stdc++.h>

template <class T>
constexpr T abs(T x) { return x < 0 ? -x : x; }

using i8 = int8_t;
using i16 = int16_t;
using i32 = int32_t;
using i64 = int64_t;
using i128 = __int128_t;
using isz = ptrdiff_t;

using u8 = uint8_t;
using u16 = uint16_t;
using u32 = uint32_t;
using u64 = uint64_t;
using u128 = __uint128_t;
using usz = size_t;

using f32 = float;
using f64 = double;
using f128 = long double;

template <class T>
using ptt = std::pair<T, T>;
template <class T>
using pt3 = std::tuple<T, T, T>;
template <class T>
using pt4 = std::tuple<T, T, T, T>;

template <class T, usz N>
using arr = std::array<T, N>;
template <class T>
using vec = std::vector<T>;
template <class T>
using vvec = vec<vec<T>>;
template <class T>
using v3ec = vec<vvec<T>>;
template <class U, class T>
using vecp = vec<std::pair<U, T>>;
template <class U, class T>
using vvecp = vvec<std::pair<U, T>>;
template <class T>
using vecpt = vec<ptt<T>>;
template <class T>
using vvecpt = vvec<ptt<T>>;

template <class T, class C = std::less<T>>
using pq = std::priority_queue<T, vec<T>, C>;
template <class T>
using pqg = std::priority_queue<T, vec<T>, std::greater<T>>;

using strn = std::string;
using strnv = std::string_view;

using vecu = vec<u32>;
using vvecu = vvec<u32>;
using v3ecu = v3ec<u32>;
using vecu64 = vec<u64>;
using vecb = vec<bool>;
using vvecb = vvec<bool>;

#ifdef ONLINE_JUDGE
#undef assert
#define assert(x) 42
#endif

using namespace std::literals;

constexpr i8 operator""_i8(unsigned long long x) { return (i8)x; }
constexpr i16 operator""_i16(unsigned long long x) { return (i16)x; }
constexpr i32 operator""_i32(unsigned long long x) { return (i32)x; }
constexpr i64 operator""_i64(unsigned long long x) { return (i64)x; }
constexpr isz operator""_iz(unsigned long long x) { return (isz)x; }

constexpr u8 operator""_u8(unsigned long long x) { return (u8)x; }
constexpr u16 operator""_u16(unsigned long long x) { return (u16)x; }
constexpr u32 operator""_u32(unsigned long long x) { return (u32)x; }
constexpr u64 operator""_u64(unsigned long long x) { return (u64)x; }
constexpr usz operator""_uz(unsigned long long x) { return (usz)x; }

inline const auto fn_0 = [](auto&&...) {};


#line 5 "src/code/graph/alist.hpp"

namespace tifa_libs::graph {

template <bool with_deg = false>
struct alist {
  using weight_type = u32;
  using value_type = vvecu;
  value_type g;
  u32 cnt_arc;
  vecu deg_in;

  //! vertex ID: [0, n)
  explicit constexpr alist(u32 n = 0) : g(n), cnt_arc(0), deg_in(0) {
    if constexpr (with_deg) deg_in.resize(n);
  }

  constexpr void add_arc(u32 u, u32 v) {
    g[u].push_back(v), ++cnt_arc;
    if constexpr (with_deg) ++deg_in[v];
  }
};
template <class G>
concept is_alist = (std::is_base_of_v<alist<true>, G> || std::is_base_of_v<alist<false>, G>);

}  // namespace tifa_libs::graph


#line 5 "src/code/tree/tree.hpp"

namespace tifa_libs::graph {

struct tree : alist<false> {
  u32 root;

  explicit constexpr tree(u32 n, u32 root = 0) : alist(n), root(root) {}
};

}  // namespace tifa_libs::graph


#line 5 "src/code/tree/centroid.hpp"

namespace tifa_libs::graph {

// @return centroid, at MOST 2
constexpr vecu tree_centroid(tree const &tr) {
  vecu sz(tr.g.size()), ans;

  auto dfs = [&](auto &&dfs, u32 now, u32 fa = -1_u32) -> void {
    sz[now] = 1;
    u32 max_sz = 0;
    for (u32 to : tr.g[now])
      if (to != fa) {
        dfs(dfs, to, now);
        sz[now] += sz[to];
        max_sz = std::max(max_sz, sz[to]);
      }
    if (std::max(max_sz, (u32)tr.g.size() - sz[now]) <= tr.g.size() / 2) ans.push_back(now);
  };

  dfs(dfs, tr.root);
  return ans;
}

}  // namespace tifa_libs::graph


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