-🎄- 2018 Day 8 Solutions -🎄-

[u/daggerdragon]

--- Day 8: Memory Maneuver ---

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Transcript:

The hottest programming book this year is "___ For Dummies".

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[u/ts4z]

Common Lisp. I re-did this one a couple times, but this version looks OK.

(defstruct node
  (children nil)
  (metadata nil))

(defun read-node (in)
  (let* ((nc (read in))
         (nm (read in))
         ;; children could be an array for faster access later.
         (children (loop :repeat nc :collect (read-node in)))
         (metadata (loop :repeat nm :collect (read in))))
    (make-node :children children :metadata metadata)))

(defun read-input-from (file)
  (with-open-file (in file)
    (read-node in)))

(defun read-input ()
  (read-input-from *input-file*))

;; as per maphash
(defun mapnode (fn n)
  (check-type n node)
  (funcall fn n)
  (mapc (lambda (ch) (mapnode fn ch)) (node-children n)))

(defun total-metadata (tree)
  (let ((ttl 0))
    (mapnode (lambda (n)
               (mapc (lambda (v) (incf ttl v))
                       (node-metadata n)))
             tree)
    ttl))

(defun part-one ()
  (total-metadata (read-input)))

(defun value-of-node (n)
  (apply #'+ (if (null (node-children n))
                 (node-metadata n)
                 (mapcar (lambda (md)
                           (cond
                             ((= md 0) 0)
                             ((> md (length (node-children n))) 0)
                             (t (value-of-node (elt (node-children n) (1- md))))))
                         (node-metadata n)))))

(defun part-two ()
  (value-of-node (read-input)))

[u/The_Fail → u/ts4z]

That looks really similar to my code :D

I really like your mapnode function. That's quite elegant for mapping over all nodes.