Day 3: Gear Ratios


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  • hades@lemm.ee
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    11 months ago

    Python

    Questions and comments welcome!

    import collections
    import re
    
    from .solver import Solver
    
    class Day03(Solver):
      def __init__(self):
        super().__init__(3)
        self.lines = []
    
      def presolve(self, input: str):
        self.lines = input.rstrip().split('\n')
    
      def solve_first_star(self):
        adjacent_to_symbols = set()
        for i, line in enumerate(self.lines):
          for j, sym in enumerate(line):
            if sym in ('0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '.'):
              continue
            for di in (-1, 0, 1):
              for dj in (-1, 0, 1):
                adjacent_to_symbols.add((i + di, j + dj))
        numbers = []
        for i, line in enumerate(self. lines):
          for number_match in re.finditer(r'\d+', line):
            is_adjacent_to_symbol = False
            for j in range(number_match.start(), number_match.end()):
              if (i, j) in adjacent_to_symbols:
                is_adjacent_to_symbol = True
            if is_adjacent_to_symbol:
              numbers.append(int(number_match.group()))
        return sum(numbers)
    
      def solve_second_star(self):
        gear_numbers = collections.defaultdict(list)
        adjacent_to_gears = {}
        for i, line in enumerate(self.lines):
          for j, sym in enumerate(line):
            if sym == '*':
              for di in (-1, 0, 1):
                for dj in (-1, 0, 1):
                  adjacent_to_gears[(i + di, j + dj)] = (i, j)
        for i, line in enumerate(self. lines):
          for number_match in re.finditer(r'\d+', line):
            adjacent_to_gear = None
            for j in range(number_match.start(), number_match.end()):
              if (i, j) in adjacent_to_gears:
                adjacent_to_gear = adjacent_to_gears[(i, j)]
            if adjacent_to_gear:
              gear_numbers[adjacent_to_gear].append(int(number_match.group()))
        ratios = []
        for gear_numbers in gear_numbers.values():
          match gear_numbers:
            case [a, b]:
              ratios.append(a * b)
        return sum(ratios)