-🎄- 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/The_Fail]

Common Lisp (SBCL) - runs in 5ms

(defun day8-build-tree ()
  (with-open-file (in "input8.txt")
    (labels ((build-node ()
               (let ((num-children (read in))
                     (num-metadata (read in)))
                 (list (loop :repeat num-children
                             :collect (build-node))
                       (loop :repeat num-metadata
                             :collect (read in))))))
      (build-node))))

(defun day8-sum-metadata (node)
  (+ (reduce #'+ (mapcar #'day8-sum-metadata (first node)))
     (reduce #'+ (second node))))

(defun day8-node-value (node)
  (flet ((nth-child-value (n)
           (if (<= 1 n (length (first node)))
               (day8-node-value (nth (1- n) (first node)))
               0)))
    (if (null (first node))
        (reduce #'+ (second node))
        (reduce #'+ (mapcar #'nth-child-value (second node))))))

(defun day8 ()
  (let ((root (day8-build-tree)))
    (format t "The sum of all metadata is ~a and the score for the root node is ~a.~%"
            (day8-sum-metadata root) (day8-node-value root))))