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

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Last update: 2022-09-11 00:53:50+09:00
Problem: https://judge.yosupo.jp/problem/cycle_detection

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Code

#define PROBLEM "https://judge.yosupo.jp/problem/cycle_detection"

#include "../../template/template.hpp"

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

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"
#define PROBLEM "https://judge.yosupo.jp/problem/cycle_detection"

#line 1 "template/template.hpp"
#include<bits/stdc++.h>

using namespace std;

using int64 = long long;
const int mod = 1e9 + 7;

const int64 infll = (1LL << 62) - 1;
const int inf = (1 << 30) - 1;

struct IoSetup {
  IoSetup() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);
    cerr << fixed << setprecision(10);
  }
} iosetup;

template< typename T1, typename T2 >
ostream &operator<<(ostream &os, const pair< T1, T2 >& p) {
  os << p.first << " " << p.second;
  return os;
}

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

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

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

template< typename T1, typename T2 >
inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }

template< typename T1, typename T2 >
inline bool chmin(T1 &a, T2 b) { return a > b && (a = b, true); }

template< typename T = int64 >
vector< T > make_v(size_t a) {
  return vector< T >(a);
}

template< typename T, typename... Ts >
auto make_v(size_t a, Ts... ts) {
  return vector< decltype(make_v< T >(ts...)) >(a, make_v< T >(ts...));
}

template< typename T, typename V >
typename enable_if< is_class< T >::value == 0 >::type fill_v(T &t, const V &v) {
  t = v;
}

template< typename T, typename V >
typename enable_if< is_class< T >::value != 0 >::type fill_v(T &t, const V &v) {
  for(auto &e : t) fill_v(e, v);
}

template< typename F >
struct FixPoint : F {
  explicit FixPoint(F &&f) : F(forward< F >(f)) {}

  template< typename... Args >
  decltype(auto) operator()(Args &&... args) const {
    return F::operator()(*this, forward< Args >(args)...);
  }
};
 
template< typename F >
inline decltype(auto) MFP(F &&f) {
  return FixPoint< F >{forward< F >(f)};
}
#line 4 "test/verify/yosupo-cycle-detection.test.cpp"

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

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

/**
 * @brief Graph Template(グラフテンプレート)
 */
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 {
  vector< vector< Edge< T > > > g;
  int es;

  Graph() = default;

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

  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;
      cin >> a >> b;
      a += padding;
      b += padding;
      T c = T(1);
      if(weighted) cin >> c;
      if(directed) add_directed_edge(a, b, c);
      else add_edge(a, b, c);
    }
  }

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

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

template< typename T = int >
using Edges = vector< Edge< T > >;
#line 4 "graph/others/cycle-detection.hpp"

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

  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)) {
        reverse(begin(cycle), end(cycle));
        return cycle;
      }
    }
    return {};
  }
};
#line 6 "test/verify/yosupo-cycle-detection.test.cpp"

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";
    }
}