Envío 4808

Código

from collections import defaultdict 

def has_cycles(g, N):
    s = set()
    for i in range(N):
        if i not in s:
            if dfs(g, i, s):
                return True
    return False

def dfs(g, node, s):
    s.add(node)
    for nn in g[node]:
        if nn in s:
            return True
        if dfs(g, nn, s):
            return True
    return False

N, M = map(int, input().split(" "))
g = defaultdict(list)
for _ in range(M):
    s, t = input().split(" ")
    g[s].append(t)
    g[t].append(s)
if has_cycles(g, N):
    print("Yes")
else:
    print("No")