Day 15: Lens Library
Megathread guidelines
- Keep top level comments as only solutions, if you want to say something other than a solution put it in a new post. (replies to comments can be whatever)
- Code block support is not fully rolled out yet but likely will be in the middle of the event. Try to share solutions as both code blocks and using something such as https://topaz.github.io/paste/ , pastebin, or github (code blocks to future proof it for when 0.19 comes out and since code blocks currently function in some apps and some instances as well if they are running a 0.19 beta)
FAQ
- What is this?: Here is a post with a large amount of details: https://programming.dev/post/6637268
- Where do I participate?: https://adventofcode.com/
- Is there a leaderboard for the community?: We have a programming.dev leaderboard with the info on how to join in this post: https://programming.dev/post/6631465
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Python
0.248 line-seconds (sixth simplest so far after days 6, 2, 1, 4 and 9).
import collections
import re
from .solver import Solver
def _hash(string: str) -> int:
result = 0
for c in string:
result = (result + ord(c)) * 17 % 256
return result
def _assert_full_match(pattern: str, string: str):
m = re.fullmatch(pattern, string)
if not m:
raise RuntimeError(f'pattern {pattern} does not match {string}')
return m
class Day15(Solver):
input: list[str]
def __init__(self):
super().__init__(15)
def presolve(self, input: str):
self.input = input.rstrip().split(',')
def solve_first_star(self) -> int:
return sum(_hash(string) for string in self.input)
def solve_second_star(self) -> int:
boxes = [collections.OrderedDict() for _ in range(256)]
for instruction in self.input:
label, op, value = _assert_full_match(r'([a-z]+)([=-])(\d*)', instruction).groups()
box = boxes[_hash(label)]
match op:
case '-':
if label in box:
del box[label]
case '=':
box[label] = value
return sum((1 + box_idx) * (1 + lens_idx) * int(value)
for box_idx, box in enumerate(boxes)
for lens_idx, (_, value) in enumerate(box.items()))