test/yosupo/Graph/Cycle-Detection(Directed).test.cpp

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Last update: 2023-11-11 17:58:53+09:00
Problem: https://judge.yosupo.jp/problem/cycle_detection

Depends on

Code

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

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

#include "../../../graph/cycle-detect.hpp"

int main(){
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  int n,m;
  cin >> n >> m;
  graph root(n);
  rep(i, m){
    int a,b;
    cin >> a >> b;
    root[a].push_back({ a, b, 1, i });
  }
  Cycle cycle(root);
  auto res = cycle.detect();
  if(res.empty()) cout << "-1\n";
  else{
    cout << res.size() << "\n";
    for(auto &x : res) cout << x.idx << "\n";
  }
}

#line 1 "test/yosupo/Graph/Cycle-Detection(Directed).test.cpp"
#define PROBLEM "https://judge.yosupo.jp/problem/cycle_detection"

#line 1 "template/template.hpp"
#include <iostream>
#include <cmath>
#include <string>
#include <vector>
#include <algorithm>
#include <tuple>
#include <cstdint>
#include <cstdio>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <deque>
#include <bitset>
#include <cctype>
#include <climits>
#include <functional>
#include <cassert>
#include <numeric>
#include <cstring>
#define rep(i, n) for(int i = 0; i < (n); i++)
#define per(i, n) for(int i = (n) - 1; i >= 0; i--)
using ll = long long;
#define vi vector<int>
#define vvi vector<vi>
#define vl vector<ll>
#define pii pair<int, int>
#define pll pair<ll, ll>
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
constexpr int mod = 1000000007;
using namespace std;
template<class T, class U>
bool chmax(T &a, const U &b){ return a < b ? (a = b, 1) : 0; }
template<class T, class U>
bool chmin(T &a, const U &b){ return a > b ? (a = b, 1) : 0; }
#line 4 "test/yosupo/Graph/Cycle-Detection(Directed).test.cpp"

#line 2 "graph/template.hpp"

/**
 * @brief Graph Template
*/
template <class T>
struct Edge {
  int from,to;
  T cost;
  int idx;
  Edge(){};
  Edge(int f, int t, T c=1, int i=-1) : from(f), to(t), cost(c), idx(i){}
  Edge(int t) : to(t), from(-1), cost(1), idx(-1){}
  operator int() const{ return to; }
  bool operator<(const Edge &e){ return cost < e.cost; }
};
template <class T>
struct Graph : vector<vector<Edge<T>>> {
  Graph(){}
  Graph(const int &n) : vector<vector<Edge<T>>>(n){}
  void add_edge(int a, int b, T c=1, int i=-1){
    (*this)[a].push_back({ a, b, c, i });
  }
};
using graph = Graph<int>;
#line 2 "graph/cycle-detect.hpp"

struct Cycle {
  Cycle(const graph &_g) : g(_g){}
  vector<Edge<int>> detect(){
    const int n = g.size();
    used.assign(n, 0);
    prev.assign(n, -1);
    for(int i = 0; i < n; i++){
      if(!used[i] && dfs(i)){
        reverse(cyc.begin(), cyc.end());
        return cyc;
      }
    }
    return {};
  }
  private:
  const graph &g;
  vector<int> used;
  vector<Edge<int>> prev, cyc;
  bool dfs(int pos){
    used[pos] = 1;
    for(const auto &x : g[pos]){
      if(!used[x]){
        prev[x] = x;
        if(dfs(x)) return true;
      }else if(used[x] == 1){
        int cur = pos;
        cyc.push_back(x);
        while(cur != x){
          cyc.push_back(prev[cur]);
          cur = prev[cur].from;
        }
        return true;
      }
    }
    used[pos] = 2;
    return false;
  }
};
#line 6 "test/yosupo/Graph/Cycle-Detection(Directed).test.cpp"

int main(){
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  int n,m;
  cin >> n >> m;
  graph root(n);
  rep(i, m){
    int a,b;
    cin >> a >> b;
    root[a].push_back({ a, b, 1, i });
  }
  Cycle cycle(root);
  auto res = cycle.detect();
  if(res.empty()) cout << "-1\n";
  else{
    cout << res.size() << "\n";
    for(auto &x : res) cout << x.idx << "\n";
  }
}