src/day02.lisp

   1 (asdf:load-system :adventofcode2020)
   2 (in-package #:adventofcode2020)
   3
   4 (defun valid-password-count? (pw-spec)
   5   (destructuring-bind (count-str char-str passwd) (split " " pw-spec)
   6     (let ((countp (destructuring-bind (count-low count-high) (mapcar #'parse-integer (split "-" count-str))
   7                     (lambda (n)
   8                       (<= count-low n count-high))))
   9           (char-count (loop with char = (char char-str 0)
  10                             for c across passwd
  11                             summing (if (char= c char) 1 0))))
  12       (funcall countp char-count))))
  13
  14 (defun valid-password-index? (pw-spec)
  15   (destructuring-bind (index-str char-str passwd) (split " " pw-spec)
  16     (let* ((indices (mapcar (compose #'1- #'parse-integer) (split "-" index-str)))
  17            (char (char char-str 0))
  18            (get-char (lambda (n) (char passwd n))))
  19       (->> (mapcar get-char indices)
  20            (remove char)
  21            (length)
  22            (= 1)))))
  23
  24 (day 02 input
  25   (let ((pws-and-specs (list-from input)))
  26     (part1 (->> pws-and-specs
  27                 (remove-if-not #'valid-password-count?)
  28                 (length)))
  29     (part2 (->> pws-and-specs
  30                 (remove-if-not #'valid-password-index?)
  31                 (length)))))
  32
  33 (def-suite day02)
  34 (in-suite day02)
  35
  36 (test valid-password-count?
  37   (is (equal
  38         '(t nil t)
  39         (mapcar #'valid-password-count?
  40                 '("1-3 a: abcde" "1-3 b: cdefg" "2-9 c: ccccccccc")))))
  41
  42 (test valid-password-index?
  43   (is (equal
  44         '(t nil nil)
  45         (mapcar #'valid-password-index?
  46                 '("1-3 a: abcde" "1-3 b: cdefg" "2-9 c: ccccccccc")))))
  47
  48 (run! 'day02)