day2.el

(defun read-lines (filePath)
  "Return a list of lines of a file at filePath."
  (with-temp-buffer
    (insert-file-contents filePath)
    (split-string (buffer-string) "\n" t)))

(defun parse-spec (s)
  (let ( (parsed  (split-string s " " t)    )  )

    (list
     (mapcar 'string-to-number (split-string (car parsed) "-"))
     (substring (nth 1 parsed) 0 1)
     (car (last parsed))

     )
  )
  )

(defun count-character-in-str (str char)
  (let ( (n-times 0) )
    (dotimes (i (length str))
      (setq n-times (+ n-times
                    (if (string=  char ( char-to-string (aref str i)))
                        1 0)
                     ))
      )
    n-times
  ))


(defun valid-password? (spec)
  (let* (
         (spec-parsed  (parse-spec  spec ))
         (n-chars-pass (count-character-in-str  (car (last spec-parsed)) (nth 1 spec-parsed) ) )
         (min-char-count (caar spec-parsed))
         (max-char-count (car (cdar spec-parsed)))
         )
    (if (and (>= n-chars-pass min-char-count  ) (<= n-chars-pass max-char-count))
        1 0)
    )
)

(let ((lines (read-lines "input02.txt")))
     (apply '+ (mapcar 'valid-password? lines))
)


(defun valid-password-2? (spec)
  (let* (
         (spec-parsed  (parse-spec  spec))
         (password-str  (car (last spec-parsed)))
         (character-to-check   (nth 1 spec-parsed) )
         (pos1 (caar spec-parsed))
         (pos2 (car (cdar spec-parsed)))
         (num-matching-characters (apply '+
                                         (list
                                          (if (string=  (char-to-string (aref password-str (- pos1 1)))  character-to-check) 1 0)
                                          (if (string=  (char-to-string (aref password-str (- pos2 1)))  character-to-check) 1 0)
                                          )
                                         ))
         )

     (if (eq num-matching-characters 1) 1 0)
    )
  )


(let ((lines (read-lines "input02.txt")))
     (apply '+ (mapcar 'valid-password-2? lines))
)