day11b.py

from collections import defaultdict

f = open('input.txt', 'r')
lines = [line.split(' ') for line in f.read().split('\n')]

neighs = defaultdict(list)
neighs |= {line[0][:-1]: line[1:] for line in lines}

nodes = list(set(list(neighs.keys())))
nodes = list(set(nodes + [node for vals in neighs.values() for node in vals]))

in_edges = defaultdict(int)
for key, values in neighs.items():
	for neigh in values:
		in_edges[neigh] += 1

def paths(start, end):
	in_e = defaultdict(int)
	in_e |= {k:v for k,v in in_edges.items()}

	count = defaultdict(int)
	count[start] = 1

	q = [node for node in nodes if in_e[node] == 0]
	while q:
		curr = q.pop()
		for neigh in neighs[curr]:
			in_e[neigh] -= 1
			count[neigh] += count[curr]

			if in_e[neigh] == 0:
				q.append(neigh)

	return count[end]

res = paths('svr', 'fft') * paths('fft', 'dac') * paths('dac', 'out')
res += paths('svr', 'dac') * paths('dac', 'fft') * paths('fft', 'out')
print(res)