test/yosupo_CycleDetection.test.cpp

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Last update: 2023-04-05 23:10:22+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 "../Graph/CycleDetection.hpp"

signed main(){
    int n,m;cin>>n>>m;
    vector<vector<int>> g(n);
    map<pair<int,int>,int> id;
    rep(i,m){
        int u,v;cin>>u>>v;
        id[{u,v}]=i;
        g[u].push_back(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_CycleDetection.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_CycleDetection.test.cpp"

#line 1 "Graph/CycleDetection.hpp"
vector<int> CycleDetection(vector<vector<int>> &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;
    };

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

signed main(){
    int n,m;cin>>n>>m;
    vector<vector<int>> g(n);
    map<pair<int,int>,int> id;
    rep(i,m){
        int u,v;cin>>u>>v;
        id[{u,v}]=i;
        g[u].push_back(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;
}