Day 14: Parabolic Reflector Dish

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

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  • hades@lemm.ee
    3·
    3 months ago

    Python

    import numpy as np

from .solver import Solver


def _tilt(row: list[int], reverse: bool = False) -> list[int]:
  res = row[::-1] if reverse else row[:]
  rock_x = 0
  for x, item in enumerate(res):
    if item == 1:
      rock_x = x + 1
    if item == 2:
      if rock_x < x:
        res[rock_x] = 2
        res[x] = 0
      rock_x += 1
  return res[::-1] if reverse else res

class Day14(Solver):
  data: np.ndarray

  def __init__(self):
    super().__init__(14)

  def presolve(self, input: str):
    lines = input.splitlines()
    self.data = np.zeros((len(lines), len(lines[0])), dtype=np.int8)
    for x, line in enumerate(lines):
      for y, char in enumerate(line):
        if char == '#':
          self.data[x, y] = 1
        elif char == 'O':
          self.data[x, y] = 2

  def solve_first_star(self) -> int:
    for y in range(self.data.shape[1]):
      self.data[:, y] = _tilt(self.data[:, y].tolist())
    return sum((self.data.shape[0] - x) * (self.data[x] == 2).sum() for x in range(self.data.shape[0]))

  def solve_second_star(self) -> int:
    seen = {}
    order = []
    for i in range(1_000_000_000):
      order += [self.data.copy()]
      s = self.data.tobytes()
      if s in seen:
        loop_size = i - seen[s]
        remainder = (1_000_000_000 - i) % loop_size
        self.data = order[seen[s] + remainder]
        break
      seen[s] = i
      for y in range(self.data.shape[1]):
        self.data[:, y] = _tilt(self.data[:, y].tolist())
      for x in range(self.data.shape[0]):
        self.data[x, :] = _tilt(self.data[x, :].tolist())
      for y in range(self.data.shape[1]):
        self.data[:, y] = _tilt(self.data[:, y].tolist(), reverse=True)
      for x in range(self.data.shape[0]):
        self.data[x, :] = _tilt(self.data[x, :].tolist(), reverse=True)
    return sum((self.data.shape[0] - x) * (self.data[x] == 2).sum() for x in range(self.data.shape[0]))

    33.938 line-seconds (ranks 3rd hardest after days 8 and 12 so far).