Envío 2661

Código

#include <bits/stdc++.h>

#define fi first
#define se second
#define forn(i,n) for(int i=0; i< (int)n; ++i)
#define for1(i,n) for(int i=1; i<= (int)n; ++i)
#define fore(i,l,r) for(int i=(int)l; i<= (int)r; ++i)
#define ford(i,n) for(int i=(int)(n) - 1; i>= 0; --i)
#define fored(i,l,r) for(int i=(int)r; i>= (int)l; --i)
#define pb push_back
#define el '\n'
#define d(x) cout<< #x<< " " << x<<el
#define ri(n) scanf("%d",&n)
#define sz(v) ((int)v.size())
#define all(v) v.begin(),v.end()
#define allr(v) v.rbegin(),v.rend()

using namespace std;

typedef long long ll;
typedef double ld;
typedef pair<int,int> ii;
typedef pair<char,int> pci;
typedef tuple<int, int, int> tiii;
typedef pair<ll,ll> pll;
typedef vector<int> vi;

const int inf = 1e9;
const int nax = 1e5+200;
const ld pi = acos(-1);
const ld eps= 1e-9;

int dr[] = {1,-1,0, 0,1,-1,-1, 1};
int dc[] = {0, 0,1,-1,1, 1,-1,-1};

vi g[nax];
int seen[nax];
bool in[nax];
bool f = false;

void dfs(int u, int c){
  seen[u] = c;
  in[u] = true;
  for(int v : g[u]){
    f |= (in[v]);
    if(!seen[v]){
      dfs(v, c);
    }
  }
  in[u] = false;
}


int main(){
  ios_base::sync_with_stdio(false);
  cin.tie(NULL); cout.tie(NULL);
  cout<< setprecision(20)<< fixed;
  int n, m;
  cin>> n>> m;
  int u, v;
  forn(i,m){
    cin>> u>> v;
    g[u].pb(v);
  }
  forn(i,n){
    if(!seen[i]){
      dfs(i, i+1);
    }
  }
  cout<< (f ? "Yes" : "No")<<el;
}