Day 4: Scratchcards


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/ or pastebin (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)

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  • @[email protected]
    link
    fedilink
    311 months ago

    Python

    Questions and feedback welcome!

    import collections
    import re
    
    from .solver import Solver
    
    class Day04(Solver):
      def __init__(self):
        super().__init__(4)
        self.cards = []
    
      def presolve(self, input: str):
        lines = input.rstrip().split('\n')
        self.cards = []
        for line in lines:
          left, right = re.split(r' +\| +', re.split(': +', line)[1])
          left, right = map(int, re.split(' +', left)), map(int, re.split(' +', right))
          self.cards.append((list(left), list(right)))
    
      def solve_first_star(self):
        points = 0
        for winning, having in self.cards:
          matches = len(set(winning) & set(having))
          if not matches:
            continue
          points += 1 << (matches - 1)
        return points
    
      def solve_second_star(self):
        factors = collections.defaultdict(lambda: 1)
        count = 0
        for i, (winning, having) in enumerate(self.cards):
          count += factors[i]
          matches = len(set(winning) & set(having))
          if not matches:
            continue
          for j in range(i + 1, i + 1 + matches):
            factors[j] = factors[j] + factors[i]
        return count