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;; Advent of Code 2020 - Day 2
(require 'cl-lib)
(require 'f)
(require 'ht)
(require 's)
(require 'seq)
(defvar day2/input
;; This one was too large to inline.
(s-lines (f-read "/tmp/aoc/day2.txt")))
(defun day2/count-letters (password)
(let ((table (ht-create)))
(cl-loop for char across password
for current = (ht-get table char)
do (ht-set table char
(if current (+ 1 current) 1)))
table))
(defun day2/parse (input)
(let* ((split (s-split " " input))
(range (s-split "-" (car split))))
(list (string-to-number (car range))
(string-to-number (cadr range))
(string-to-char (cadr split))
(caddr split))))
(defun day2/count-with-validation (func)
(length (-filter
(lambda (password)
(and (not (seq-empty-p password))
(apply func (day2/parse password))))
day2/input)))
;; Puzzle 1
(defun day2/validate-oldjob (min max char password)
(let ((count (ht-get (day2/count-letters password) char)))
(when count
(and (>= count min)
(<= count max)))))
(message "Solution to day2/1: %s"
(day2/count-with-validation #'day2/validate-oldjob))
;; Puzzle 2
(defun day2/validate-toboggan (pos1 pos2 char password)
(xor (= char (aref password (- pos1 1)))
(= char (aref password (- pos2 1)))))
(message "Solution to day2/2: %s"
(day2/count-with-validation #'day2/validate-toboggan))
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