Envío 4809

Código

from collections import defaultdict, deque

def has_cycles(N, g):
	in_deg = defaultdict(int)
	for n in g:
		for nn in g[n]:
			in_deg[nn] += 1

	q = deque([i for i in range(N) if in_deg[i] == 0])
	res = 0

	while q:
		node = q.popleft()
		res += 1
		for nn in g[node]:
			in_deg[nn] -= 1
			if in_deg[nn] == 0:
				q.append(nn)

	return res != N





N, M = map(int, input().split(" "))
g = defaultdict(set)
for _ in range(M):
	s, t = map(int, input().split(" "))
	g[s].add(t)

if has_cycles(N, g):
	print("Yes")
else:
	print("No")