Language: C++

//#define NDEBUG
#include <algorithm>
#include <cstddef>
#include <cstdint>
#include <iostream>
#include <utility>
#include <vector>

namespace n91 {

using i8 = std::int_fast8_t;
using i32 = std::int_fast32_t;
using i64 = std::int_fast64_t;
using u8 = std::uint_fast8_t;
using u32 = std::uint_fast32_t;
using u64 = std::uint_fast64_t;
using isize = std::ptrdiff_t;
using usize = std::size_t;

struct rep {
  struct itr {
    usize i;
    constexpr itr(const usize i) noexcept : i(i) {}
    void operator++() noexcept { ++i; }
    constexpr usize operator*() const noexcept { return i; }
    constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
  };
  const itr f, l;
  constexpr rep(const usize f, const usize l) noexcept
      : f(std::min(f, l)), l(l) {}
  constexpr auto begin() const noexcept { return f; }
  constexpr auto end() const noexcept { return l; }
};
struct revrep {
  struct itr {
    usize i;
    constexpr itr(const usize i) noexcept : i(i) {}
    void operator++() noexcept { --i; }
    constexpr usize operator*() const noexcept { return i; }
    constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
  };
  const itr f, l;
  constexpr revrep(const usize f, const usize l) noexcept
      : f(l - 1), l(std::min(f, l) - 1) {}
  constexpr auto begin() const noexcept { return f; }
  constexpr auto end() const noexcept { return l; }
};
template <class T> auto md_vec(const usize n, const T &value) {
  return std::vector<T>(n, value);
}
template <class... Args> auto md_vec(const usize n, Args... args) {
  return std::vector<decltype(md_vec(args...))>(n, md_vec(args...));
}
template <class T> constexpr T difference(const T &a, const T &b) noexcept {
  return a < b ? b - a : a - b;
}
template <class T> void chmin(T &a, const T &b) noexcept {
  if (b < a)
    a = b;
}
template <class T> void chmax(T &a, const T &b) noexcept {
  if (a < b)
    a = b;
}
template <class F> class rec_lambda {
  F f;

public:
  rec_lambda(F &&f) : f(std::move(f)) {}
  template <class... Args> auto operator()(Args &&... args) const {
    return f(*this, std::forward<Args>(args)...);
  }
};
template <class F> auto make_rec(F &&f) { return rec_lambda<F>(std::move(f)); }
template <class T> T scan() {
  T ret;
  std::cin >> ret;
  return ret;
}

} // namespace n91

#include "data_structure/union_find.cpp"

#include <string>

namespace n91 {

void main_() {
  /*
  std::ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
  //*/
  const usize n = scan<usize>();
  union_find uf(n * 2);
  for (const usize i : rep(0, n - 1)) {
    const usize a = scan<usize>() - 1;
    const usize b = scan<usize>() - 1;
    uf.unite(a, n + b);
    uf.unite(n + a, b);
  }
  auto buc = md_vec(2, 0, usize());
  for (const usize i : rep(0, n)) {
    buc[uf.same(0, i)].push_back(i);
  }
  if (buc[0].size() < buc[1].size()) {
    std::swap(buc[0], buc[1]);
  }
  std::vector<usize> cn(3, 0);
  for (const usize i : rep(0, n)) {
    cn[(i + 1) % 3] += 1;
  }
  auto ans = md_vec(3, 0, usize());
  if (buc[0].size() >= cn[1] + cn[2]) {
    for (const usize i : rep(0, cn[1])) {
      ans[1].push_back(buc[0][i]);
    }
    for (const usize i : rep(cn[1], cn[1] + cn[2])) {
      ans[2].push_back(buc[0][i]);
    }
    for (const usize i : rep(cn[1] + cn[2], buc[0].size())) {
      ans[0].push_back(buc[0][i]);
    }
    for (const usize i : rep(0, buc[1].size())) {
      ans[0].push_back(buc[1][i]);
    }
  } else if (buc[0].size() >= cn[1] && buc[1].size() >= cn[2]) {
    for (const usize i : rep(0, cn[1])) {
      ans[1].push_back(buc[0][i]);
    }
    for (const usize i : rep(0, cn[2])) {
      ans[2].push_back(buc[1][i]);
    }
    for (const usize i : rep(cn[1], buc[0].size())) {
      ans[0].push_back(buc[0][i]);
    }
    for (const usize i : rep(cn[2], buc[1].size())) {
      ans[0].push_back(buc[1][i]);
    }
  } else {
    assert(false);
  }
  for (const usize i : rep(1, n + 1)) {
    const usize t = i % 3;
    std::cout << ans[t].back() + 1 << " ";
    ans[t].pop_back();
  }
}

} // namespace n91

int main() {
  n91::main_();
  return 0;
}


Compiler output:
a.cc:83:10: fatal error: data_structure/union_find.cpp: No such file or directory
   83 | #include "data_structure/union_find.cpp"
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.