Envío 2671

Código

#include <bits/stdc++.h>
#define ii              pair<int,int>
#define F               first
#define S               second
#define pb              push_back
#define all(x)          (x).begin(),(x).end()
#define rall(x)         (x).rbegin(),(x).rend()
#define fore(i, a, b)   for(int i = a; i < b; i += 1)
#define forr(i, a)      for(int i = a; i >= 0; i--)
#define sz(s)           int(s.size())
#define cls(a,car)      memset(a,car,sizeof (a))
#define db(x)           cout << #x << " is " << x << '\n'
#define angle(x)        double(x * acos(-1) / 180.0)
using namespace std;
void debug(){cout << endl;}
template<typename T, typename... Args>
void debug(T a, Args... args){cout << a << " "; debug(args...);}
typedef long long   ll;
typedef vector<int> vi;
typedef vector<ii>  vii;
const int N = 1e4 + 10;
const ll mod = 1e9 + 7;
const double E = 1e-7;
vi G[N];
int vis[N];
bool flag;
void dfs(int u){
    for(auto v : G[u]){
        if(vis[v] == -1){
            vis[v] = 1;
            dfs(v);
            vis[v] = 2;
        }
        else{
            if(vis[v] == 1)
                flag = 1;
        }
    }
}
void solve(){
    int n, m, u, v;
    cin >> n >> m;
    while(m--){
        cin >> u >> v;
        G[u].pb(v);
    }
    cls(vis, -1);
    for(int i = 0; i < n; i++)
        if(vis[i] == -1){
            vis[i] = 1;
            dfs(i);
        }

    cout << (flag ? "Yes" : "No") << '\n';
}
int main(){
    #ifdef LOCAL
        freopen("input.txt", "r", stdin);
        freopen("output.txt", "w", stdout);
    #else
       ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    #endif
    int t = 1;
    //cin >> t;
    for(int i = 1; i <= t; i++){
        solve();
    }

    #ifdef LOCAL
        cerr << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " s.\n";
    #endif
    return 0;
}