Advent of Code 2020 day 23
Advent of Code 2020 day 23. Ooh I liked this one because it taught me something new: linked lists!
I took the “obvious” approach for part one, but almost nothing of that version is shown below as I first re-factored it, then stuck part_two_answer on top of it.
import unittest
class Game():
def __init__(self, starting_circle, part=1):
starting_circle = [int(char) for char in starting_circle]
self.max_cup = max(starting_circle)
self.min_cup = min(starting_circle)
if part == 2:
starting_circle += [ i for i in range(self.max_cup + 1, 1_000_000 + 1)]
self.max_cup = 1_000_000
self.circle = {
cup: starting_circle[(i + 1) % len(starting_circle)]
for i, cup in enumerate(starting_circle)
}
self.length = len(self.circle)
self.current_cup = starting_circle[0]
def move(self):
crab = [
self.circle[self.current_cup],
self.circle[self.circle[self.current_cup]],
self.circle[self.circle[self.circle[self.current_cup]]]
]
destination = self.current_cup - 1
if destination < self.min_cup:
destination = self.max_cup
while destination in crab:
destination -= 1
if destination < self.min_cup:
destination = self.max_cup
destination_original_link = self.circle[destination]
chain_end_original_link = self.circle[crab[-1]]
self.circle[destination] = crab[0]
self.circle[crab[-1]] = destination_original_link
self.circle[self.current_cup] = chain_end_original_link
self.current_cup = chain_end_original_link
def part_one_answer(self):
cup = 1
result = ""
for i in range(self.length - 1):
result += str(self.circle[cup])
cup = self.circle[cup]
return result
def part_two_answer(self):
return self.circle[1] * self.circle[self.circle[1]]
def part_one(input):
game = Game(input)
for _ in range(100):
game.move()
return game.part_one_answer()
def part_two(input):
game = Game(input, 2)
for _ in range(10_000_000):
game.move()
return game.part_two_answer()
class TestPartOne(unittest.TestCase):
def test_part_one_example(self):
self.assertEqual(part_one("389125467"), '67384529')
class TestPartTwo(unittest.TestCase):
def test_part_two_example(self):
self.assertEqual(part_two("389125467"), 149245887792)
if __name__ == '__main__':
print(f"Part one: {part_one(INPUT)}")
print(f"Part two: {part_two(INPUT)}")