Envío 4109

Código

//
#include <bits/stdc++.h>
using namespace std;
#define INF 1000000000
#define MOD 1000000007
#define PI 3.14159265
#define EPS 1e-9
#define Pi acos(-1.0)
typedef pair<int, int> ii;
typedef long long ll;
typedef vector<ll> vll;
typedef pair<ll,ll> pll;
#define forr(i,a,b) for(int i=(a); i<(b); i++)
#define clean(arr,val) memset(arr,val,sizeof(arr))
#define forn(i,n) forr(i,0,n)
#define PB push_back
typedef vector<int> vi;
typedef vector<ii> vii;
typedef vector<pll> vpll;

/*CODE START HERE*/

int n, m;
vector<vi> AdjList;
bool ans, visited[10005];
map<ii,bool> appear;

void bfs(int x){
    queue<int> q;
    q.push(x);
    while(!q.empty()){
        int u = q.front();
        q.pop();
        visited[u] = 1;
        for(int i = 0; i < (int)AdjList[u].size(); i++){
            int v = AdjList[u][i];
            if(visited[v]){
                ans = true;
            }else{
                q.push(v);
            }
        }
    }
    
}

int main(){
    ios::sync_with_stdio(0);
    cin >> n >> m;
    AdjList.assign(n,vi());
    int u, v;
    ans = false;
    appear.clear();
    forn(i,m){
        cin >> u >> v;
        ii temp = ii(u,v);
        if(appear.find(temp) == appear.end()){
            appear[temp] = true;
            AdjList[u].push_back(v);
        }
    }
    clean(visited,0);
    forn(i,n){
        if(!visited[i]){
            bfs(i);
        }
    }
    if(ans){
        cout << "Yes\n";
    }else{
        cout << "No\n";
    }
    return 0;
}