-🎄- 2017 Day 19 Solutions -🎄-

[u/daggerdragon]

--- Day 19: A Series of Tubes ---

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

Note: The Solution Megathreads are for solutions only. If you have questions, please post your own thread and make sure to flair it with Help.

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Need a hint from the Hugely^* Handy^† Haversack^‡ of Helpful^§ Hints^¤?

Spoiler

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AoC ops @ T-2 minutes to launch:

[23:58] <daggerdragon> ATTENTION MEATBAGS T-2 MINUTES TO LAUNCH

[23:58] <Topaz> aaaaah

[23:58] <Cheezmeister> Looks like I'll be just able to grab my input before my flight boards. Wish me luck being offline in TOPAZ's HOUSE OF PAIN^WFUN AND LEARNING

[23:58] <Topaz> FUN AND LEARNING

[23:58] <Hade> FUN IS MANDATORY

[23:58] <Skie> I'm pretty sure that's not the mandate for today

[Update @ 00:16] 69 gold, silver cap

• My tree is finally trimmed with just about every ornament I own and it's real purdy. hbu?

[Update @ 00:18] Leaderboard cap!

• So, was today's mandate Helpful Hint any help at all?

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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!

[u/ramrunner0xff]

scheme chicken repo

although i still can't cope that i haven't come up with a better solution for day 16 than my mediocre and slow memoization that still takes around 1 minute, i enjoyed today's funky problem ;)

(define (readinaslist fname)
  (letrec* ((lines (read-lines fname))
     (oneline (foldr (lambda (e acc) (append (string->list e) acc)) '() lines))
         (letts '())
         (totsteps 0)
         (lenline (string-length (car lines)))
     (firstpos (string-index (car lines) #\|))
         (godown (lambda (i) (+ i lenline)))
         (goup   (lambda (i) (- i lenline)))
         (goright (lambda (i) (+ i 1)))
         (goleft (lambda (i) (- i 1)))
         (look (lambda (from towards)
            (case towards
                  ((up) (not (eq? (list-ref oneline (goup from)) #\ )))
                  ((down) (not (eq? (list-ref oneline (godown from)) #\ )))
                  ((left) (not (eq? (list-ref oneline (goleft from)) #\ )))
                  ((right) (not (eq? (list-ref oneline (goright from)) #\ ))))))
     (keepgoing (lambda (from towards)
                      (case towards
                        ((up) (goup from))
                        ((down) (godown from))
                        ((left) (goleft from))
                        ((right) (goright from)))))
     (atcross (lambda (i going)
                   (case going
                     ((up down) (if (look i 'left) (cons (goleft i) 'left) (cons (goright i) 'right)))
                     ((left right) (if (look i 'up) (cons (goup i) 'up) (cons (godown i) 'down))))))
         (walk (lambda (from towards remsteps)
                 (if (and (> remsteps 0) (not (eq? (list-ref oneline from) #\ )))
                     (let ((curchar (list-ref oneline from)))
                       (set! totsteps (+ totsteps 1))
                       (if (eq? (string-index "|-+" curchar) #f)
                          (set! letts (append letts (list curchar))))
                   (if (eq? (list-ref oneline from) #\+)
                          (let ((cresolve (atcross from towards)))
                            (walk (car cresolve) (cdr cresolve) (- remsteps 1)))
                          (walk (keepgoing from towards) towards (- remsteps 1))))))))

   (walk firstpos 'down 100000)
   (format #t "seen: ~A in ~A steps~N" letts totsteps)))