68 lines
2.1 KiB
Python
68 lines
2.1 KiB
Python
from __future__ import annotations
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import itertools
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import math
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from typing import Optional
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from .aoc import Aoc2, AocSameParser
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class Map:
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def __init__(self, inpt: str) -> None:
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lines = inpt.splitlines()
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self.directions: list[int] = [0 if rl == "L" else 1 for rl in lines[0]]
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self.rules = {line[:3]: (line[7:10], line[12:15]) for line in lines[2:]}
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class Day08(AocSameParser[Map], Aoc2[Map, Map]):
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def parseinput(self, inpt: str) -> Map:
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return Map(inpt)
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def part1(self, inpt: Map) -> int:
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current = "AAA"
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for steps, direction in enumerate(itertools.cycle(inpt.directions)):
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if current == "ZZZ":
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return steps
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else:
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current = inpt.rules[current][direction]
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raise RuntimeError("End of the rainbow")
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def find_loop(self, list_of_nrs: list[int]) -> Optional[tuple[int, int]]:
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for index in range(len(list_of_nrs)):
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for index in range(len(list_of_nrs[index + 1 :])):
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diff = list_of_nrs[index + 1] - list_of_nrs[index]
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if list_of_nrs[index + 1] + diff in list_of_nrs:
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return list_of_nrs[index], diff
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return None
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def part2(self, inpt: Map) -> int:
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current = [node for node in inpt.rules.keys() if node.endswith("A")]
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steps_to_z = [[] for _ in current]
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loops: list[Optional[tuple[int, int]]] = [None for _ in current]
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for steps, direction in enumerate(itertools.cycle(inpt.directions)):
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for n, node in enumerate(current):
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if node.endswith("Z"):
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steps_to_z[n].append(steps)
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loops[n] = self.find_loop(steps_to_z[n])
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if not any(loop is None for loop in loops):
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break
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else:
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current = [inpt.rules[node][direction] for node in current]
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# Turns out, each path directly loops :/
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return math.lcm(*(loop[0] for loop in loops if loop is not None))
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def main() -> None:
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day08 = Day08(2023, 8)
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day08._example_code_nr1 = 1
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day08._example_code_nr2 = -1
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day08.run()
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if __name__ == "__main__":
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main()
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