src/day02.lisp

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