Advent of Code day 12 part 1 recursive version

AoC_2021_12_1.recurs.py

"""
Advent of Code 2021 day 12 part 1.
This version makes use of recursive function calls to implement
depth-first-search.
"""
from collections import defaultdict


def count_paths(caves_seen):
    path_count = 0
    cave = caves_seen[-1]
    for adj in adjacents[cave]:
        if adj in caves_seen and adj.islower():
            continue
        if adj == "end":
            path_count += 1
        else:
            path_count += count_paths(caves_seen + [adj])
    return path_count


adjacents = defaultdict(set)
with open("input_12.txt") as f:
    for line in f:
        c1, c2 = tuple(line.strip().split("-"))
        adjacents[c1].add(c2)
        adjacents[c2].add(c1)

print(count_paths(["start"]))