test/verify/yosupo-cycle-detection.test.cpp

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• Last update: 2026-08-10 14:28:01+00:00
• Problem: https://judge.yosupo.jp/problem/cycle_detection

Depends on

• Graph Template (グラフテンプレート) (graph/graph-template.hpp)
• Cycle Detection (閉路検出) (graph/others/cycle-detection.hpp)

Code

// clang-format off
// competitive-verifier: PROBLEM https://judge.yosupo.jp/problem/cycle_detection
// clang-format on

#include <iostream>

#include "../../graph/others/cycle-detection.hpp"

using namespace std;

int main() {
  int N, M;
  cin >> N >> M;
  CycleDetection<> g(N);
  g.read(M, 0, false, true);
  auto ret = g.build();
  if (ret.empty()) {
    cout << -1 << "\n";
  } else {
    cout << ret.size() << "\n";
    for (auto& e : ret) cout << e.idx << "\n";
  }
}

#line 1 "test/verify/yosupo-cycle-detection.test.cpp"
// clang-format off
// competitive-verifier: PROBLEM https://judge.yosupo.jp/problem/cycle_detection
// clang-format on

#include <iostream>

#line 2 "graph/others/cycle-detection.hpp"

#include <algorithm>
#include <iterator>
#include <vector>

#line 2 "graph/graph-template.hpp"

#include <cstddef>
#line 6 "graph/graph-template.hpp"

template <typename T = int>
struct Edge {
  int from, to;
  T cost;
  int idx;

  Edge() = default;

  Edge(int from, int to, T cost = 1, int idx = -1)
      : from(from), to(to), cost(cost), idx(idx) {}

  operator int() const { return to; }
};

template <typename T = int>
struct Graph {
  std::vector<std::vector<Edge<T> > > g;
  int es;

  Graph() = default;

  explicit Graph(int n) : g(n), es(0) {}

  std::size_t size() const { return g.size(); }

  void add_directed_edge(int from, int to, T cost = 1) {
    g[from].emplace_back(from, to, cost, es++);
  }

  void add_edge(int from, int to, T cost = 1) {
    g[from].emplace_back(from, to, cost, es);
    g[to].emplace_back(to, from, cost, es++);
  }

  void read(int M, int padding = -1, bool weighted = false,
            bool directed = false) {
    for (int i = 0; i < M; i++) {
      int a, b;
      std::cin >> a >> b;
      a += padding;
      b += padding;
      T c = T(1);
      if (weighted) std::cin >> c;
      if (directed)
        add_directed_edge(a, b, c);
      else
        add_edge(a, b, c);
    }
  }

  inline std::vector<Edge<T> >& operator[](const int& k) { return g[k]; }

  inline const std::vector<Edge<T> >& operator[](const int& k) const {
    return g[k];
  }
};

template <typename T = int>
using Edges = std::vector<Edge<T> >;
#line 8 "graph/others/cycle-detection.hpp"

/**
 * @brief Cycle Detection(閉路検出)
 *
 */
template <typename T = int>
struct CycleDetection : Graph<T> {
  using Graph<T>::Graph;
  using Graph<T>::g;

  std::vector<int> used;
  Edges<T> pre, cycle;

  bool dfs(int idx) {
    used[idx] = 1;
    for (auto& e : g[idx]) {
      if (used[e] == 0) {
        pre[e] = e;
        if (dfs(e)) return true;
      } else if (used[e] == 1) {
        int cur = idx;
        while (cur != e) {
          cycle.emplace_back(pre[cur]);
          cur = pre[cur].from;
        }
        cycle.emplace_back(e);
        return true;
      }
    }

    used[idx] = 2;
    return false;
  }

  Edges<T> build() {
    used.assign(g.size(), 0);
    pre.resize(g.size());
    for (int i = 0; i < (int)g.size(); i++) {
      if (used[i] == 0 && dfs(i)) {
        std::reverse(std::begin(cycle), std::end(cycle));
        return cycle;
      }
    }
    return {};
  }
};
#line 8 "test/verify/yosupo-cycle-detection.test.cpp"

using namespace std;

int main() {
  int N, M;
  cin >> N >> M;
  CycleDetection<> g(N);
  g.read(M, 0, false, true);
  auto ret = g.build();
  if (ret.empty()) {
    cout << -1 << "\n";
  } else {
    cout << ret.size() << "\n";
    for (auto& e : ret) cout << e.idx << "\n";
  }
}

Test cases

Env	Name	Status	Elapsed	Memory
g++	example_00	AC	2 ms	4 MB
g++	example_01	AC	1 ms	4 MB
g++	example_02	AC	1 ms	4 MB
g++	long_cycle_00	AC	234 ms	60 MB
g++	long_cycle_01	AC	187 ms	49 MB
g++	random_00	AC	126 ms	31 MB
g++	random_01	AC	138 ms	35 MB
g++	random_02	AC	95 ms	16 MB
g++	random_03	AC	13 ms	23 MB
g++	random_04	AC	32 ms	18 MB
g++	random_05	AC	128 ms	27 MB
g++	random_06	AC	82 ms	30 MB
g++	random_07	AC	6 ms	8 MB
g++	random_08	AC	91 ms	23 MB
g++	random_09	AC	53 ms	13 MB
g++	random_dag_00	AC	155 ms	31 MB
g++	random_dag_01	AC	147 ms	34 MB
g++	random_dag_02	AC	98 ms	16 MB
g++	random_dag_03	AC	13 ms	23 MB
g++	random_dag_04	AC	33 ms	18 MB
g++	random_dag_05	AC	132 ms	27 MB
g++	random_dag_06	AC	80 ms	30 MB
g++	random_dag_07	AC	6 ms	8 MB
g++	random_dag_08	AC	107 ms	23 MB
g++	random_dag_09	AC	54 ms	13 MB
g++	random_dag_dense_00	AC	67 ms	13 MB
g++	random_dag_dense_01	AC	70 ms	12 MB
g++	random_dag_dense_02	AC	66 ms	13 MB
g++	random_dag_dense_03	AC	70 ms	12 MB
g++	random_dag_dense_04	AC	83 ms	14 MB
g++	random_dense_00	AC	74 ms	15 MB
g++	random_dense_01	AC	69 ms	14 MB
g++	random_dense_02	AC	64 ms	14 MB
g++	random_dense_03	AC	69 ms	14 MB
g++	random_dense_04	AC	78 ms	13 MB
clang++	example_00	AC	2 ms	4 MB
clang++	example_01	AC	1 ms	4 MB
clang++	example_02	AC	2 ms	4 MB
clang++	long_cycle_00	AC	299 ms	77 MB
clang++	long_cycle_01	AC	185 ms	55 MB
clang++	random_00	AC	125 ms	31 MB
clang++	random_01	AC	195 ms	35 MB
clang++	random_02	AC	103 ms	16 MB
clang++	random_03	AC	14 ms	23 MB
clang++	random_04	AC	33 ms	18 MB
clang++	random_05	AC	134 ms	28 MB
clang++	random_06	AC	99 ms	30 MB
clang++	random_07	AC	6 ms	8 MB
clang++	random_08	AC	110 ms	23 MB
clang++	random_09	AC	52 ms	13 MB
clang++	random_dag_00	AC	160 ms	31 MB
clang++	random_dag_01	AC	156 ms	34 MB
clang++	random_dag_02	AC	95 ms	16 MB
clang++	random_dag_03	AC	13 ms	23 MB
clang++	random_dag_04	AC	32 ms	18 MB
clang++	random_dag_05	AC	140 ms	27 MB
clang++	random_dag_06	AC	85 ms	29 MB
clang++	random_dag_07	AC	6 ms	8 MB
clang++	random_dag_08	AC	120 ms	23 MB
clang++	random_dag_09	AC	54 ms	13 MB
clang++	random_dag_dense_00	AC	67 ms	13 MB
clang++	random_dag_dense_01	AC	65 ms	12 MB
clang++	random_dag_dense_02	AC	66 ms	13 MB
clang++	random_dag_dense_03	AC	67 ms	12 MB
clang++	random_dag_dense_04	AC	77 ms	14 MB
clang++	random_dense_00	AC	67 ms	15 MB
clang++	random_dense_01	AC	66 ms	14 MB
clang++	random_dense_02	AC	64 ms	14 MB
clang++	random_dense_03	AC	66 ms	14 MB
clang++	random_dense_04	AC	77 ms	13 MB

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