Advent of Code day 18 part 1

AoC_2021_18_1.py

"""
This is essentially @benediktwerner's solution.  I only did a few
renames and refactoring to get to understand how it works.
"""

import json
import functools


def add(n1, n2):
    return reduction([n1, n2])


def reduction(num):
    while True:
        _, num, _, exploded = ignite(num)
        if not exploded:
            num, splitted = split(num)
            if not splitted:
                break
    return num


def lsum(tail, t):
    if t is None:
        return tail
    if isinstance(tail, int):
        return tail + t
    return [lsum(tail[0], t), tail[1]]


def rsum(head, h):
    if h is None:
        return head
    if isinstance(head, int):
        return head + h
    return [head[0], rsum(head[1], h)]


def ignite(num, depth=0):
    if isinstance(num, int):
        return None, num, None, False
    if depth == 4:
        return num[0], 0, num[1], True
    pre, mid0, post, exploded = ignite(num[0], depth + 1)
    if exploded:
        return pre, [mid0, lsum(num[1], post)], None, True
    pre, mid1, post, exploded = ignite(num[1], depth + 1)
    if exploded:
        return None, [rsum(mid0, pre), mid1], post, True
    return None, num, None, False


def split(num):
    if isinstance(num, int):
        if num < 10:
            return num, False
        return [(num // 2), num - (num // 2)], True
    head, splitted = split(num[0])
    if splitted:
        return [head, num[1]], True
    tail, splitted = split(num[1])
    if splitted:
        return [num[0], tail], True
    return num, False


def magn(num):
    m0 = num[0] if isinstance(num[0], int) else magn(num[0])
    m1 = num[1] if isinstance(num[1], int) else magn(num[1])
    return 3 * m0 + 2 * m1


lines = open("input_18.txt").read().splitlines()
total = functools.reduce(add, map(json.loads, lines))
print(magn(total))