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day08.py
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day08.py
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"""Advent of Code 2023 - Day 08."""
import math
import re
import sys
from typing import Callable, TextIO
def parse(file: TextIO) -> tuple[str, dict[str, tuple[str, str]]]:
def parse_node(line: str):
m = re.match(r"([A-Z0-9]{3}) = \(([A-Z0-9]{3}), ([A-Z0-9]{3})\)", line)
return m.group(1), (m.group(2), m.group(3))
instructions, _, *nodes = list(line.strip() for line in file)
nodes = dict(map(parse_node, nodes))
return instructions, nodes
def find_distance(instructions: str, nodes: dict[str, tuple[str, str]], start: str, is_end: Callable[[str], bool]):
current = start
i = 0
while not is_end(current):
left, right = nodes[current]
match instructions[i % len(instructions)]:
case "L":
current = left
case "R":
current = right
i += 1
return i
def part_one(file: TextIO) -> int:
instructions, nodes = parse(file)
return find_distance(instructions, nodes, "AAA", lambda n: n == "ZZZ")
def part_two(file: TextIO) -> int:
instructions, nodes = parse(file)
starting_nodes = list(filter(lambda n: n[-1] == "A", nodes.keys()))
distances = list(find_distance(instructions, nodes, node, lambda n: n[-1] == "Z") for node in starting_nodes)
return math.lcm(*distances)
def main():
filename = sys.argv[0].replace(".py", ".txt")
with open(filename, encoding="utf-8") as file:
print("Part one:", part_one(file))
with open(filename, encoding="utf-8") as file:
print("Part two:", part_two(file))
if __name__ == "__main__":
main()