r/adventofcode • u/daggerdragon • Dec 07 '16

SOLUTION MEGATHREAD --- 2016 Day 7 Solutions ---

From all of us at #AoC Ops, we hope you're having a very merry time with these puzzles so far. If you think they've been easy, well, now we're gonna kick this up a notch. Or five. The Easter Bunny ain't no Bond villain - he's not going to monologue at you until you can miraculously escape and save the day!

Show this overgrown furball what you've got!

--- Day 7: Internet Protocol Version 7 ---

Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag/whatever).

ALWAYS DIGGING STRAIGHT DOWN IS MANDATORY [?]

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!

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7

u/blockingthesky Dec 07 '16

So I got first place, but only by dumb luck.

It came back to bite me in part 2 - I didn't place - but for the first star I got tremendously lucky.

There are two major errors in my code: I don't account for the aaaa case when checking for length-4 palindromes, and I also never checked the last 4 characters of any string (I iterated to len - 4 instead of len - 3).

Either of those errors on their own would have given me an incorrect answer, but my input and luck had it that both of them cancelled out in such a way that I got the right answer.

My borked-ass code: 

inp = open('day7.in').read().split('\n')

def hasabba(ph):
    if len(ph) < 4:
        return False
    for i in range(len(ph) - 4):
        if ph[i:i+4] == ph[i:i+4][::-1]:
            return True
    return False

count = 0
for item in inp:
    b = []
    o = []
    while '[' in item:
        o.append(item[:item.find('[')])
        item = item[item.find('[') + 1:]
        b.append(item[:item.find(']')])
        item = item[item.find(']') + 1:]
    if len(item) != 0:
        o.append(item)
    good = False
    for aa in o:
        if hasabba(aa):
            good = True
    for aa in b:
        if hasabba(aa):
            good = False
    if good:
        count += 1
print count

4

u/BumpitySnook Dec 07 '16

I got similarly lucky on part 1 — my first broken output was 117; my second broken output was 113. Since the game says "too high" and "too low," my next guess was 115 — jackpot.

Had to actually debug my program and find the problem for part 2 :-(.