test/yosupo_CycleDetection2.test.cpp

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Last update: 2023-07-17 18:02:31+09:00
Problem: https://judge.yosupo.jp/problem/cycle_detection

Depends on

Code

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

#include "../template.hpp"

#include "../Graph2/CycleDetection.hpp"

signed main(){
    int n,m;cin>>n>>m;
    Graph g(n);
    map<pair<int,int>,int> id;
    rep(i,m){
        int u,v;cin>>u>>v;
        id[{u,v}]=i;
        g.add_directed_edge(u,v);
    }
    auto res=CycleDetection(g);
    if(res.empty()){
        cout<<-1<<endl;
        return 0;
    }
    int p=res[0];
    vector<int> ans;
    for(int i=1;i<(int)res.size();i++){
        ans.push_back(id[{p,res[i]}]);
        p=res[i];
    }
    ans.push_back(id[{p,res[0]}]);
    cout<<ans.size()<<"\n";
    for(auto e:ans) cout<<e<<"\n";
    return 0;
}

#line 1 "test/yosupo_CycleDetection2.test.cpp"
#define PROBLEM "https://judge.yosupo.jp/problem/cycle_detection"

#line 1 "template.hpp"
#include<bits/stdc++.h>
using namespace std;
#define ALL(x) begin(x),end(x)
#define rep(i,n) for(int i=0;i<(n);i++)
#define debug(v) cout<<#v<<":";for(auto x:v){cout<<x<<' ';}cout<<endl;
#define mod 1000000007
using ll=long long;
const int INF=1000000000;
const ll LINF=1001002003004005006ll;
int dx[]={1,0,-1,0},dy[]={0,1,0,-1};
// ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
template<class T>bool chmax(T &a,const T &b){if(a<b){a=b;return true;}return false;}
template<class T>bool chmin(T &a,const T &b){if(b<a){a=b;return true;}return false;}

struct IOSetup{
    IOSetup(){
        cin.tie(0);
        ios::sync_with_stdio(0);
        cout<<fixed<<setprecision(12);
    }
} iosetup;
 
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==(int)v.size()?"":" ");
    return os;
}
template<typename T>
istream &operator>>(istream &is,vector<T>&v){
    for(T &x:v)is>>x;
    return is;
}

#line 4 "test/yosupo_CycleDetection2.test.cpp"

#line 1 "Graph2/GraphTemplate.hpp"



// graph template
// ref : https://ei1333.github.io/library/graph/graph-template.hpp
template<typename T=int>
struct Edge{
    int from,to;
    T w;
    int idx;
    Edge()=default;
    Edge(int from,int to,T w=1,int idx=-1):from(from),to(to),w(w),idx(idx){}
    operator int() const{return to;}
};

template<typename T=int>
struct Graph{
    vector<vector<Edge<T>>> g;
    int V,E;
    Graph()=default;
    Graph(int n):g(n),V(n),E(0){}

    int size(){
        return (int)g.size();
    }
    void resize(int k){
        g.resize(k);
        V=k;
    }
    inline const vector<Edge<T>> &operator[](int k)const{
        return (g.at(k));
    }
    inline vector<Edge<T>> &operator[](int k){
        return (g.at(k));
    }
    void add_directed_edge(int from,int to,T cost=1){
        g[from].emplace_back(from,to,cost,E++);
    }
    void add_edge(int from,int to,T cost=1){
        g[from].emplace_back(from,to,cost,E);
        g[to].emplace_back(to,from,cost,E++);
    }
    void read(int m,int pad=-1,bool weighted=false,bool directed=false){
        for(int i=0;i<m;i++){
            int u,v;cin>>u>>v;
            u+=pad,v+=pad;
            T w=T(1);
            if(weighted) cin>>w;
            if(directed) add_directed_edge(u,v,w);
            else         add_edge(u,v,w);
        }
    }
};


#line 2 "Graph2/CycleDetection.hpp"

template<typename T>
vector<int> CycleDetection(Graph<T> &g){
    int n=(int)g.size();
    vector<int> check(n,0),cyc,pre(n,-1);

    function<bool(int)> dfs=[&](int cur){
        check[cur]=1;
        for(auto &to:g[cur]){
            if(check[to]==0){
                pre[to]=cur;
                if(dfs(to)) return true;
            }else if(check[to]==1){// detect
                int v=cur;
                while(v!=to){
                    cyc.push_back(v);
                    v=pre[v];
                }
                cyc.push_back(v);
                return true;
            }
        }
        check[cur]=2;
        return false;
    };

    for(int i=0;i<n;i++){
        if(check[i]==0){
            if(dfs(i)){
                reverse(begin(cyc),end(cyc));
                return cyc;
            }
        }
    }
    return {};
}
#line 6 "test/yosupo_CycleDetection2.test.cpp"

signed main(){
    int n,m;cin>>n>>m;
    Graph g(n);
    map<pair<int,int>,int> id;
    rep(i,m){
        int u,v;cin>>u>>v;
        id[{u,v}]=i;
        g.add_directed_edge(u,v);
    }
    auto res=CycleDetection(g);
    if(res.empty()){
        cout<<-1<<endl;
        return 0;
    }
    int p=res[0];
    vector<int> ans;
    for(int i=1;i<(int)res.size();i++){
        ans.push_back(id[{p,res[i]}]);
        p=res[i];
    }
    ans.push_back(id[{p,res[0]}]);
    cout<<ans.size()<<"\n";
    for(auto e:ans) cout<<e<<"\n";
    return 0;
}