part12.py

"""https://adventofcode.com/2021/day/18"""

import re


def parse_snailfish(n):
    v = re.split(r"(\[|\]|,)", n)
    v = [x for x in v if x not in ("", ",")]
    v = [int(x) if x.isdigit() else x for x in v]
    return v


def add(a, b):
    return ["["] + a + b + ["]"]


def explode(n):
    depth = 0
    for i, s in enumerate(n):
        if s == "[":
            depth += 1
        elif s == "]":
            depth -= 1

        if (
            depth > 4
            and s == "["
            and isinstance(n[i + 1], int)
            and isinstance(n[i + 2], int)
            and n[i + 3] == "]"
        ):
            for j in range(i, 0, -1):
                if isinstance(n[j], int):
                    n[j] += n[i + 1]
                    break
            for j in range(i + 4, len(n)):
                if isinstance(n[j], int):
                    n[j] += n[i + 2]
                    break
            n = n[:i] + [0] + n[i + 4 :]
            return n, True
    return n, False


def split(n):
    for i, s in enumerate(n):
        if isinstance(s, int) and s >= 10:
            n = n[:i] + ["[", s // 2, s - s // 2, "]"] + n[i + 1 :]
            return n, True
    return n, False


def reduce(n):
    to_reduce = True
    while to_reduce:
        n, to_reduce = explode(n)
        if not to_reduce:
            n, to_reduce = split(n)
    return n


def magnitude(n):
    while len(n) > 1:
        for i, s in enumerate(n):
            if (
                s == "["
                and isinstance(n[i + 1], int)
                and isinstance(n[i + 2], int)
                and n[i + 3] == "]"
            ):
                n = n[:i] + [3 * n[i + 1] + 2 * n[i + 2]] + n[i + 4 :]
                break
    return n[0]


data = open("day-18/input", "r", encoding="utf-8").read().splitlines()

# Part 1
m = parse_snailfish(data[0])
for d in data[1:]:
    n = parse_snailfish(d)
    m = add(m, n)
    m = reduce(m)
print(magnitude(m))

# Part 2
max_magnitude = 0
for d1 in data:
    for d2 in data:
        if d1 != d2:
            m = parse_snailfish(d1)
            n = parse_snailfish(d2)
            mag = magnitude(reduce(add(m, n)))
            max_magnitude = max(max_magnitude, mag)
print(max_magnitude)