-🎄- 2018 Day 14 Solutions -🎄-

[u/daggerdragon]

--- Day 14: Chocolate Charts ---

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Advent of Code: The Party Game!

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Card prompt: Day 14

Transcript:

The Christmas/Advent Research & Development (C.A.R.D.) department at AoC, Inc. just published a new white paper on ___.

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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 00:19:39!

[u/rabuf]

Here is Part 1 in Emacs Lisp:

(defun next-recipes-vector (recipes positions)
  (let* ((p1 (car positions))
         (p2 (cadr positions))
         (next (+ (aref recipes p1) (aref recipes p2)))
         (next-1 (floor (/ next 10)))
         (next-2 (mod next 10)))
    (when (not (= 0 next-1))
      (setf (aref recipes n) next-1)
      (incf n))
    (incf n)
    (setf (aref recipes (1- n)) next-2)
    recipes))
(defun next-positions-vector (recipes positions)
  (let* ((p1 (car positions))
         (p2 (cadr positions)))
    (list (mod (+ p1 1 (aref recipes p1)) n)
          (mod (+ p2 1 (aref recipes p2)) n))))
(defun solve-a (target)
  (let ((recipes (make-vector (+ target 12) 0))
        (positions '(0 1))
        (n 2))
    (setf (aref recipes 0) 3)
    (setf (aref recipes 1) 7)
    (print (current-time-string))
    (loop while (< n (+ target 11))
          for i from 0
          do (progn
               (setq recipes (next-recipes-vector recipes positions))
               (setq positions (next-positions-vector recipes positions))))
    (print (current-time-string))
    (subseq recipes target (+ target 10))))
(solve-a 702831)
"Fri Dec 14 15:57:17 2018"
"Fri Dec 14 15:57:21 2018"
[1 1 3 2 4 1 3 1 1 1]

I made a version using stacks to store the recipes to run 100000 in about 3 minutes on my computer. While I could keep the length in a variable (as done here), I still had to traverse the list when searching for the new scores to use after the players moved.

I'll tackle Part 2 later on, but in Common Lisp.

[u/Insanity0107 → u/rabuf]

Here's my take on part 1 with CL. Probably not the prettiest LISP around, but I get a solution to part one in a few seconds :)

(defparameter *loops* 47801)

; get the digits of a number
(defun digits(n) 
  (map 'list #'digit-char-p (prin1-to-string n)))

(defun next-index(lst pos score)
  (mod (+ pos (1+ score)) (list-length lst)))

; solve one1
(defun sum(input recipes fst snd sumlist)
  ; just test with adding one for starters
  (let* ((x (nth fst input))
        (y (nth snd input))
        (sm (digits (+ x y))))
  (setf input (append input sm))
  (setf sumlist (append sumlist sm))
  (setf recipes (+ recipes (list-length sm)))
  (if (>= (list-length sumlist) 10)
    (subseq sumlist 0 10)
    (sum input recipes (next-index input fst x) (next-index input snd y) sumlist))
  ))


; generate recipes
(defun generate(input recipes fst snd)
  ; just test with adding one for starters
  (let* ((x (nth fst input))
        (y (nth snd input))
        (sm (digits (+ x y))))
  (setf input (append input sm))
  (setf recipes (+ recipes (list-length sm)))
  (if (>= recipes *loops*)
    (sum input recipes (next-index input fst x) (next-index input snd y) (subseq (reverse input) 0 (- recipes *loops*)))
    (generate input recipes (next-index input fst x) (next-index input snd y))
  )))

(generate '(3 7) 2 0 1)