#668645 (C++17(gcc12)) No.1553 Lovely City

• 問題: No.1553 Lovely City
• ユーザー: keijak
• 提出日時: 2021-06-20 21:50:35
• 言語: C++17(gcc12) (gcc 12.4.0 + boost 1.89.0)
• 結果: RE
• 実行時間: -
• コード長: 4,683 bytes
• コンパイル時間: 2,642 ms
• コンパイル使用メモリ: 225,792 KB
• 実行使用メモリ: 30,592 KB
• 最終ジャッジ日時: 2026-06-21 04:21:47
• 合計ジャッジ時間: 11,270 ms
• ジャッジサーバーID （参考情報）: judge1_1 / judge2_0

ファイルパターン	結果
sample	AC * 2
other	WA * 1 RE * 25

ソースコード

#include <bits/stdc++.h>
#define REP_(i, a_, b_, a, b, ...) \
  for (int i = (a), END_##i = (b); i < END_##i; ++i)
#define REP(i, ...) REP_(i, __VA_ARGS__, __VA_ARGS__, 0, __VA_ARGS__)
#define ALL(x) std::begin(x), std::end(x)
using i64 = long long;

template <typename T, typename U>
inline bool chmax(T &a, U b) {
  return a < b and ((a = std::move(b)), true);
}
template <typename T, typename U>
inline bool chmin(T &a, U b) {
  return a > b and ((a = std::move(b)), true);
}
template <typename T>
inline int ssize(const T &a) {
  return (int)std::size(a);
}

template <typename T>
std::istream &operator>>(std::istream &is, std::vector<T> &a) {
  for (auto &x : a) is >> x;
  return is;
}
template <typename T, typename U>
std::ostream &operator<<(std::ostream &os, const std::pair<T, U> &a) {
  return os << "(" << a.first << ", " << a.second << ")";
}
template <typename Container>
std::ostream &print_seq(const Container &a, std::string_view sep = " ",
                        std::string_view ends = "\n",
                        std::ostream &os = std::cout) {
  auto b = std::begin(a), e = std::end(a);
  for (auto it = std::begin(a); it != e; ++it) {
    if (it != b) os << sep;
    os << *it;
  }
  return os << ends;
}
template <typename T, typename = void>
struct is_iterable : std::false_type {};
template <typename T>
struct is_iterable<T, std::void_t<decltype(std::begin(std::declval<T>())),
                                  decltype(std::end(std::declval<T>()))>>
    : std::true_type {};

template <typename T, typename = std::enable_if_t<
                          is_iterable<T>::value &&
                          !std::is_same<T, std::string_view>::value &&
                          !std::is_same<T, std::string>::value>>
std::ostream &operator<<(std::ostream &os, const T &a) {
  return print_seq(a, ", ", "", (os << "{")) << "}";
}

#ifdef ENABLE_DEBUG
#include "debug_dump.hpp"
#else
#define DUMP(...)
#endif

using namespace std;

struct UnionFind {
  int n;
  mutable std::vector<int> parent;  // positive: parent, negative: size
  int num_roots;

  explicit UnionFind(int sz) : n(sz), parent(sz, -1), num_roots(sz) {}

  bool unite(int x, int y) {
    x = find(x), y = find(y);
    if (x == y) return false;
    if (-parent[x] < -parent[y]) std::swap(x, y);
    parent[x] += parent[y];
    parent[y] = x;
    --num_roots;
    return true;
  }

  int find(int v) const {
    if (parent[v] < 0) return v;
    return parent[v] = find(parent[v]);
  }

  int size(int v) const { return -parent[find(v)]; }

  bool same(int x, int y) const { return find(x) == find(y); }

  std::vector<int> roots() const {
    std::vector<int> res;
    res.reserve(num_roots);
    for (int i = 0; i < n; ++i) {
      if (parent[i] < 0) res.push_back(i);
    }
    return res;
  }
};

// Returns the topogically sorted list of nodes.
// Nodes with zero indegree come first.
// Returns nullopt if the input graph is not a DAG.
// Args:
//   g[a] = {b, c, d}; // directed adjacency list {a->b, a->c, a->d}
optional<vector<int>> topological_sort(const vector<vector<int>> &g) {
  const int n = g.size();
  vector<int> indeg(n);
  for (int v = 0; v < n; ++v) {
    for (auto u : g[v]) ++indeg[u];
  }
  deque<int> q;
  for (int v = 0; v < n; ++v) {
    if (indeg[v] == 0) {
      q.emplace_back(v);
    }
  }
  vector<int> res;
  while (not q.empty()) {
    auto v = q.front();
    q.pop_front();
    res.push_back(v);
    for (auto u : g[v]) {
      if (--indeg[u] == 0) {
        q.push_back(u);
      }
    }
  }
  if (int(res.size()) != n) {
    return nullopt;  // not a DAG
  }
  return res;
}

auto solve() -> void {
  int n, m;
  cin >> n >> m;
  vector<vector<int>> g(n);
  UnionFind uf(n);
  REP(i, m) {
    int u, v;
    cin >> u >> v;
    --u, --v;
    g[u].push_back(v);
    uf.unite(u, v);
  }

  map<int, vector<int>> components;
  REP(i, n) { components[uf.find(i)].push_back(i); }

  vector<pair<int, int>> edges;
  for (const auto &[r, nodes] : components) {
    if (ssize(nodes) <= 1) continue;
    vector<vector<int>> p(nodes.size());
    for (auto v : nodes) {
      p[v] = g[v];
    }
    auto topo = topological_sort(p);
    if (topo.has_value()) {
      const auto &vs = topo.value();
      REP(j, 1, ssize(vs)) { edges.emplace_back(vs[j - 1], vs[j]); }
    } else {
      REP(j, 1, ssize(nodes)) {
        edges.emplace_back(nodes[j - 1], nodes[j]);
        edges.emplace_back(nodes.back(), nodes.front());
      }
    }
  }

  cout << ssize(edges) << "\n";
  for (auto &[a, b] : edges) {
    cout << a + 1 << " " << b + 1 << "\n";
  }
}

int main() {
  ios_base::sync_with_stdio(false), cin.tie(nullptr);
  int t = 1;
  REP(test_case, t) { solve(); }
}