mirror of
https://github.com/Crocmagnon/advent-of-code.git
synced 2024-05-04 02:45:11 +02:00
116 lines
3.2 KiB
Python
116 lines
3.2 KiB
Python
import functools
|
|
import math
|
|
from typing import Dict
|
|
|
|
|
|
def main(filename: str, expected_part_1: int = None, expected_part_2: int = None):
|
|
print(f"\n+ Running on {filename}")
|
|
with open(filename) as f:
|
|
notes = f.read().strip().split("\n")
|
|
|
|
counter_part_1 = solve_part_1(notes)
|
|
|
|
print(f"1. Found {counter_part_1}")
|
|
if expected_part_1:
|
|
assert expected_part_1 == counter_part_1
|
|
|
|
counter_part_2 = solve_part_2(notes)
|
|
print(f"2. Found {counter_part_2}")
|
|
if expected_part_2:
|
|
assert expected_part_2 == counter_part_2
|
|
|
|
|
|
def solve_part_1(notes) -> int:
|
|
earliest = int(notes[0])
|
|
buses = map(int, filter(lambda bus: bus != "x", notes[1].split(",")))
|
|
min_delta = math.inf
|
|
min_bus = None
|
|
for bus in buses:
|
|
delta = math.ceil(earliest / bus) * bus - earliest
|
|
if delta < min_delta:
|
|
min_delta = delta
|
|
min_bus = bus
|
|
|
|
return min_bus * min_delta
|
|
|
|
|
|
def solve_part_2(notes) -> int:
|
|
split = notes[1].split(",")
|
|
modulos = []
|
|
remainders = []
|
|
for position, bus_index in enumerate(split):
|
|
if bus_index == "x":
|
|
continue
|
|
bus_index = int(bus_index)
|
|
modulos.append(bus_index)
|
|
remainders.append(bus_index - position)
|
|
return chinese_remainder(modulos, remainders)
|
|
|
|
|
|
def chinese_remainder(modulos, remainders):
|
|
"""List of modulos, then list of remainders"""
|
|
# https://rosettacode.org/wiki/Chinese_remainder_theorem#Python
|
|
# License: https://www.gnu.org/licenses/old-licenses/fdl-1.2.html
|
|
total = 0
|
|
prod = functools.reduce(lambda a, b: a * b, modulos)
|
|
for modulo, remainder in zip(modulos, remainders):
|
|
p = prod // modulo
|
|
total += remainder * mul_inv(p, modulo) * p
|
|
return total % prod
|
|
|
|
|
|
def mul_inv(a, b):
|
|
# https://rosettacode.org/wiki/Chinese_remainder_theorem#Python
|
|
# License: https://www.gnu.org/licenses/old-licenses/fdl-1.2.html
|
|
b0 = b
|
|
x0, x1 = 0, 1
|
|
if b == 1:
|
|
return 1
|
|
while a > 1:
|
|
q = a // b
|
|
a, b = b, a % b
|
|
x0, x1 = x1 - q * x0, x0
|
|
if x1 < 0:
|
|
x1 += b0
|
|
return x1
|
|
|
|
|
|
if __name__ == "__main__":
|
|
n = [3, 5, 7]
|
|
a = [2, 3, 2]
|
|
print(chinese_remainder(n, a))
|
|
|
|
|
|
def solve_part_2_iterative(notes) -> int:
|
|
"""Works but far too slow for the real deal."""
|
|
split = notes[1].split(",")
|
|
buses = list(map(int, filter(lambda bus: bus != "x", split)))
|
|
minutes = {} # type: Dict[int, int]
|
|
biggest_bus = max(buses)
|
|
biggest_bus_index = split.index(str(biggest_bus))
|
|
|
|
for bus in buses:
|
|
minutes[split.index(str(bus)) - biggest_bus_index] = bus
|
|
|
|
found = False
|
|
timestamp = 99999999999628
|
|
while not found:
|
|
timestamp += biggest_bus
|
|
found = True
|
|
for delta, bus in minutes.items():
|
|
if (timestamp + delta) % bus != 0:
|
|
found = False
|
|
break
|
|
|
|
return timestamp + min(minutes.keys())
|
|
|
|
|
|
if __name__ == "__main__":
|
|
main("inputs/day13-test1", 295, 1068781)
|
|
main("inputs/day13-test2", None, 3417)
|
|
main("inputs/day13-test3", None, 754018)
|
|
main("inputs/day13-test4", None, 779210)
|
|
main("inputs/day13-test5", None, 1261476)
|
|
main("inputs/day13-test6", None, 1202161486)
|
|
main("inputs/day13", 4315, 556100168221141)
|