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-;; -*- lexical-binding: t; -*-
-;; Advent of Code 2019 - Day 4
-
-(require 'cl-lib)
-(require 'dash)
-
-;; Puzzle 1
-
-(defun day4/to-digits (num)
-  "Convert NUM to a list of its digits."
-  (cl-labels ((steps (n digits)
-                     (if (= n 0) digits
-                       (steps (/ n 10) (cons (% n 10) digits)))))
-    (steps num '())))
-
-(defvar day4/input (-map #'day4/to-digits (number-sequence 128392 643281)))
-
-(defun day4/filter-password (digits)
-  "Determines whether the given rules match the supplied
-  number."
-
-  (and
-   ;; It is a six digit number
-   (= 6 (length digits))
-
-   ;; Value is within the range given in puzzle input
-   ;; (noop because the range is generated from the input)
-
-   ;; Two adjacent digits are the same (like 22 in 122345).
-   (car (-reduce-from (-lambda ((acc . prev) next)
-                        (cons (or acc (= prev next)) next))
-                      '(nil . 0) digits))
-
-   ;; Going from left to right, the digits never decrease; they only
-   ;; ever increase or stay the same (like 111123 or 135679).
-   (car (-reduce-from (-lambda ((acc . prev) next)
-                        (cons (and acc (>= next prev)) next))
-                      '(t . 0) digits))))
-
-;; Puzzle 2
-;;
-;; Additional criteria: If there's matching digits, they're not in a group.
-
-(cl-defstruct day4/acc state prev count)
-
-(defun day4/filter-longer-groups (digits)
-  (let ((res (-reduce-from
-              (lambda (acc next)
-                (cond ;; sequence is broken and count was at 1 ->
-                 ;; match!
-                 ((and (= (day4/acc-count acc) 2)
-                       (/= (day4/acc-prev acc) next))
-                  (setf (day4/acc-state acc) t))
-
-                 ;; sequence continues, counter increment!
-                 ((= (day4/acc-prev acc) next)
-                  (setf (day4/acc-count acc) (+ 1 (day4/acc-count acc))))
-
-                 ;; sequence broken, reset counter
-                 ((/= (day4/acc-prev acc) next)
-                  (setf (day4/acc-count acc) 1)))
-
-                (setf (day4/acc-prev acc) next)
-                acc)
-              (make-day4/acc :prev 0 :count 0) digits)))
-    (or (day4/acc-state res)
-        (= 2 (day4/acc-count res)))))
-
-(let* ((simple (-filter #'day4/filter-password day4/input))
-       (complex (-filter #'day4/filter-longer-groups simple)))
-  (message "Solution to day4/1: %d" (length simple))
-  (message "Solution to day4/2: %d" (length complex)))
-