Envío 4929

Código

/// Write by Daniel Perez .PERAPRO
#include<bits/stdc++.h>

using namespace std;
#define fast_io ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define pb push_back
#define ff first
#define ss second
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
using vi=vector<int>;
using vl=vector<ll>;
using pii=pair<int,int>;
char el = '\n';
char esp = ' ';

template<class T> bool ckmin(T& a, const T& b) { return b < a ? a = b, 1 : 0; }
template<class T> bool ckmax(T& a, const T& b) { return a < b ? a = b, 1 : 0; }

ostream& operator<<(ostream& os, const vector<int> &v){
    for(auto const &i: v){
        os<<i<<" ";
    }
    os<<'\n';
    return os;
}
string yes="Yes";
string no="No";

const int N=1e4+5;
set<int> g[N];
int color[N];
int n,m;

int cycle_start, cycle_end;

bool dfs(int v){
    color[v]=1;
    for(int u:g[v]){
        if(!color[u]){
            if(dfs(u))
                return 1;
        }else if(color[u] == 1){
            return 1;
        }
    }
    color[v] =2;
    return 0;
}

int main(){
	fast_io;
	/*
 	freopen("input.txt","r",stdin);
    freopen("output.txt","w",stdout);
    */
    int a,b;
    cin>>n>>m;
    bool f=0;
    for(int i=0;i<m;i++){
        cin>>a>>b;
        f|=(a == b);
        g[a].insert(b);
    }
    
    for(int i=0;i<n;i++){
        if(color[i] == 0 && dfs(i))
            f=1;
    }
    
    if(f)
        cout<<yes<<el;
    else 
        cout<<no<<el;
    
}

/*

*/