day23part2.py

import sys
from collections import defaultdict
from functools import cache

neighbors = defaultdict(lambda: set())
nodes = set()
for line in sys.stdin:
    a,b = line.strip().split('-')
    neighbors[a].add(b)
    neighbors[b].add(a)
    nodes.add(a)
    nodes.add(b)

@cache
def doit(ns):
    return max(map(lambda p: frozenset([p]) | doit(ns & neighbors[p]), ns), key=len, default=frozenset())

print(','.join(sorted(doit(frozenset(nodes)))))