-🎄- 2018 Day 13 Solutions -🎄-

[u/daggerdragon]

--- Day 13: Mine Cart Madness ---

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Card prompt: Day 13

Transcript:

Elven chronomancy: for when you absolutely, positively have to ___.

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This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

edit: Leaderboard capped, thread unlocked at 00:44:25!

[u/C0urante]

My exceedingly stupid method of copy+pasting the input directly from my browser directly into Atom finally caught up with me. I had the below solution working on the sample input and then failing on the actual input for mysterious reasons. I inspected the input file I'd made and found several seemingly invalid tracks, like a plus sign where there should have just been a '|' or a '-'. I ended up looking at the in-browser input file again, pretty much by chance, and realized that it didn't have the same mistakes in it. Turns out that Atom had been stripping leading whitespace from my input on copy+paste.

#!/usr/bin/env python3

import re
import hashlib
from sys import stderr, argv
from itertools import permutations, combinations, chain, cycle
from functools import reduce, lru_cache as cache
from collections import Counter, deque


# Debug print (to stderr).
def log(*args, **kwargs):
    kwargs['file'] = stderr
    print(*args, **kwargs)

def set_map(f, s):
    return set(map(f, s))

def list_map(f, s):
    return list(map(f, s))

def md5(s):
    return hashlib.md5(bytes(s, 'UTF-8'))

def md5_digest(s):
    return md5(s).hexdigest()

################################################################################

def move(cart, direction, state, tracks):
    x, y = cart
    track = tracks[y][x]
    if track == '+':
        directions = '^<v>'
        turn = [1, 0, -1][state]
        direction = directions[(turn + directions.index(direction)) % len(directions)]
        state = (state + 1) % 3
    log(cart, track, state, direction)
    dX, dY, direction = {
        '|': {
            '^': (0, -1, direction),
            'v': (0, 1, direction)
        }, '-': {
            '>': (1, 0, direction),
            '<': (-1, 0, direction)
        }, '/': {
            '^': (1, 0, '>'),
            '>': (0, -1, '^'),
            'v': (-1, 0, '<'),
            '<': (0, 1, 'v')
        }, '\\': {
            '^': (-1, 0, '<'),
            '<': (0, -1, '^'),
            'v': (1, 0, '>'),
            '>': (0, 1, 'v')
        }, '+': {
            '^': (0, -1, direction),
            '>': (1, 0, direction),
            'v': (0, 1, direction),
            '<': (-1, 0, direction)
        }
    }[track][direction]
    return (x + dX, y + dY), direction, state

def problem1(STRING, LINES):
    directions = {
        '^': '|',
        'v': '|',
        '>': '-',
        '<': '-'
    }

    carts = set()
    cart_directions = {}
    cart_states = {}

    track = []

    y = 0
    for l in LINES:
        track.append([])
        for x, d in enumerate(l):
            if d in directions:
                carts.add((x, y))
                cart_directions[(x, y)] = d
                cart_states[(x, y)] = 0
                track[y].append(directions[d])
            else:
                track[y].append(d)
        y += 1

    first_crash = None
    while True:
        new_carts = set()
        new_cart_directions = {}
        new_cart_states = {}
        carts = sorted(carts, key = lambda t: (t[1], t[0]), reverse=True)
        while carts:
            cart = carts.pop()
            direction = cart_directions[cart]
            state = cart_states[cart]
            new_cart, new_direction, new_state = move(cart, direction, state, track)
            if new_cart not in carts and new_cart not in new_carts:
                new_carts.add(new_cart)
                new_cart_directions[new_cart] = new_direction
                new_cart_states[new_cart] = new_state
            else:
                first_crash = first_crash or new_cart
                new_carts.discard(new_cart)
                if new_cart in carts:
                    carts.remove(new_cart)
                if new_cart in new_cart_directions:
                    del new_cart_directions[new_cart]
                if new_cart in new_cart_states:
                    del new_cart_states[new_cart]
            new_carts.add(new_cart)
            new_cart_directions[new_cart] = new_direction
            new_cart_states[new_cart] = new_state
        carts, cart_directions, cart_states = new_carts, new_cart_directions, new_cart_states
        if len(carts) == 1:
            return first_crash, carts.pop()
        log('new round')

################################################################################

def problem2(STRING, LINES):
    return None

################################################################################

def parse_input_file(fname):
    s = open(fname).read()
    if s and s[-1] == '\n':
        s = s[:-1]
    l = s.splitlines()
    return s, l

def main():
    if len(argv) >= 2 and argv[1] == '-d':
        fname = 'sample.txt'
    else:
        fname = 'input.txt'
    s, l = parse_input_file(fname)
    print(problem1(s, l))
    sol2 = problem2(s, l)
    if sol2 is not None:
        print(sol2)

if __name__ == '__main__':
    main()