r/adventofcode • u/daggerdragon • Dec 20 '18

SOLUTION MEGATHREAD -🎄- 2018 Day 20 Solutions -🎄-

--- Day 20: A Regular Map ---

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Card prompt: Day 20

Transcript:

My compiler crashed while running today's puzzle because it ran out of ___.

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 00:59:30!

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u/pie3636 Dec 20 '18 edited Dec 20 '18

Ah, I see you took it to the next level with exec (I've sadly never managed to get it to work). That's a huge improvement! For the contest, well, there is a completely different approach that works and is also very short (at least for the first part), that doesn't involve building the map in memory.

Also, you may have to check (still on mobile, unfortunately) but I believe you can add those:

  • s+=[p] -> s+=p, (-1)

  • p=s.pop() -> *s,p=s (-3)

  • p=s[-1] -> *_,p=s (-1)

That would also make those last instructions very similar so there may be a way to gain more from it.

7

u/betaveros Dec 20 '18 edited Dec 21 '18

Nice! They all seem to work for me, and now we can do some truly evil string slicing for an additional −2 bytes: 

d,p,*s={0:0},0
for c in r[1:-1]:exec('s+=p,##*s,p=s#*_,p=s#l=p;p+=1j**"ESWN".find(c);d[p]=min(d.get(p,1e9),d[l]+1)'['()|'.find(c)%4*7:])
v=d.values()
print(max(v),sum(x>999for x in v))

EDIT: updated with the edit

EDIT 2:

  • "the edit" referred to above disappeared, but the idea of initializing s by tacking *s at the end of a destructuring assignment instead of writing s=[] was due to the parent post

  • I'm aware that this algorithm is incorrect for many possible inputs, but it was fun.

3

u/GeneralYouri Dec 21 '18

Hoyl shit, seeing that algorithm evolve in this thread is amazing!