My solution for day 5 of the 2024 Advent of Code. I couldn't wrap my head around how to order the instructions correctly in part 2, so I thought "why not simply let Python sort it out for me ;)".

aoc2024day5.py

from collections import defaultdict

with open(r'day_5') as f:
    data = f.read()

first_part, second_part = data.split("\n\n")

first_part = [element.split("|") for element in first_part.split("\n")]
first_part = [[int(element) for element in rule] for rule in first_part]

second_part = second_part.split("\n")
second_part = [[int(element) for element in instruction.split(",")] for instruction in second_part]

# --- part 1 ---

rules = defaultdict(set)

for rule in first_part:
    first, second = rule
    rules[first].add(second)

faulty_instructions = []


def calculate_middle_values(instructions, rules):
    result = 0
    for instruction in second_part:
        for index, num in enumerate(instruction):
            if index == len(instruction) - 1:  # last element reached
                result += instruction[len(instruction) // 2]  # add value of middle num to result
            if not set(instruction[index + 1:]) <= rules[num]:
                faulty_instructions.append(instruction)  # could be used for part 2
                break
    return result


print(calculate_middle_values(second_part, rules))

# --- part 2 ---

class Position:
    # use a class attribute to share it among all instances.
    rules = defaultdict(set)

    def __init__(self, num):
        self.num = num

    def __lt__(self, other):
        """if the other's number is in the corresponding set of self.num, return True"""
        return other.num in self.rules[self.num]

first_part, second_part = data.split("\n\n")

first_part = [element.split("|") for element in first_part.split("\n")]
first_part = [[int(element) for element in rule] for rule in first_part]

# fill the Position's rules attribute
for rule in first_part:
    first, second = rule
    Position.rules[first].add(second)

second_part = second_part.split("\n")
second_part = [[Position(int(element)) for element in instruction.split(",")] for instruction in second_part]

result = 0

for instruction in second_part:
    for i, num in enumerate(instruction):
        # faulty = None
        if any(num > (faulty := other_num) for other_num in instruction[i + 1:]):
            # print([num.num for num in instruction])
            # print(f"faulty instruction found: {num.num=} and {faulty.num=}\n\n")
            sorted_instruction = sorted(instruction)
            value_of_num = sorted_instruction[len(sorted_instruction) // 2].num
            result += value_of_num
            break

print(result)