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🎄 - 2023 DAY 15 SOLUTIONS -🎄

Day 15: Lens Library

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4 comments

  • Nim

    Almost caught up. Not much to say about this one. Part 1 was a freebie. Part 2 had a convoluted description, but was still pretty easy.

  • C

    Yes, it's a hash table. Did I pick a language with built in hash tables? Of course I didn't. Could I have used one of the many libraries implementing one? Sure. But the real question is, can we make do with stuffing things into a few static arrays at nearly zero memory and runtime cost? Yes!

    In the spirit of Fred Brooks, it’ll suffice here to show my data structures:

    struct slot { char label[8]; int lens; };
struct box { struct slot slots[8]; int nslots; };

static struct box boxes[256];

    https://github.com/sjmulder/aoc/blob/master/2023/c/day15.c

  • This felt ... too simple. I think the hardest part of part two for me was reading comprehension. My errors were typically me not reading exactly was there.

    Python 
    import re
import math
import argparse
import itertools

def int_hash(string:str) -> int:
    hash = 0
    for c in [*string]:
        hash += ord(c)
        hash *= 17
        hash = hash % 256
    return hash

class Instruction:
    def __init__(self,string:str) -> None:
        label,action,strength = re.split('([-=])',string)
        self.label = label
        self.action = action
        if not strength:
            strength = 0
        self.strength = int(strength)
    
    def __repr__(self) -> str:
        return f"Instruction(l={self.label}, a={self.action}, s={self.strength})"
    
    def __str__(self) -> str:
        stren = str(self.strength if self.strength > 0 else '')
        return f"{self.label}{self.action}{stren}"


class Lens:
    def __init__(self,label:str,focal_length:int) -> None:
        self.label:str = label
        self.focal_length:int = focal_length

    def __repr__(self) -> str:
        return f"Lens(label:{self.label},focal_length:{self.focal_length})"
    
    def __str__(self) -> str:
        return f"[{self.label} {self.focal_length}]"

def main(line_list:str,part:int):
    init_sequence = line_list.splitlines(keepends=False)[0].split(',')
    sum = 0
    focal_array = dict[int,list[Lens]]()
    for i in range(0,256):
        focal_array[i] = list[Lens]()
    for s in init_sequence:
        hash_value = int_hash(s)
        sum += hash_value

        # part 2 stuff
        action = Instruction(s)
        position = int_hash(action.label)
        current_list = focal_array[position]
        existing_lens = list(filter(lambda x:x.label == action.label,current_list))
        if len(existing_lens) > 1:
            raise Exception("multiple of same lens in box, what do?")
        match action.action:
            case '-':
                if len(existing_lens) == 1:
                    current_list.remove(existing_lens[0])
            case '=':
                if len(existing_lens) == 0:
                    current_list.append(Lens(action.label,action.strength))
                if len(existing_lens) == 1:
                    existing_lens[0].focal_length = action.strength
            case _:
                raise Exception("unknown action")

    print(f"Part1: {sum}")
    #print(focal_array)

    sum2 = 0
    for i,focal_box in focal_array.items():
        for l,lens in enumerate(focal_box):
            sum2 += ( (i+1) * (l+1) * lens.focal_length )

    print(f"Part2: {sum2}")


if __name__ == "__main__":
    parser = argparse.ArgumentParser(description="template for aoc solver")
    parser.add_argument("-input",type=str)
    parser.add_argument("-part",type=int)
    args = parser.parse_args()
    filename = args.input
    if filename == None:
        parser.print_help()
        exit(1)
    part = args.part
    file = open(filename,'r')
    main(file.read(),part)
    file.close()

  • 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()))