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;;;; 2015.01.01-first-attempt.lisp
;;;; Advent of Code 2015 Day 1, Attempt 1
;;;; First attempt in Common Lisp
;; ---------------------------------------------------------------------
;;; Package Definition
;; ---------------------------------------------------------------------
(defpackage :2015-01-first-attempt
(:use #:common-lisp))
(in-package :2015-01-first-attempt)
;; ---------------------------------------------------------------------
;;; Definitions
;; ---------------------------------------------------------------------
(defparameter *PUZZLE-INPUT-FILE* "~/proj/Learn/aoc/src/2015.01._PUZZLE-INPUT.txt"
"File to be used as input to the program.")
(defparameter *PUZZLE-INPUT-STRING* (uiop:read-file-string *PUZZLE-INPUT-FILE*)
"String version of the text in `*PUZZLE-INPUT-FILE*'.")
(defparameter *PUZZLE-INPUT* (loop for char across *PUZZLE-INPUT-STRING*
collect char)
"Puzzle input in lisp list form.")
;; ---------------------------------------------------------------------
;;; Part 1
;; -------
;; Santa is trying to deliver presents in a large apartment building, but
;; he can't find the right floor - the directions he got are a little
;; confusing. He starts on the ground floor (floor 0) and then follows
;; the instructions one character at a time.
;;
;; An opening parenthesis, (, means he should go up one floor, and a
;; closing parenthesis, ), means he should go down one floor.
;;
;; The apartment building is very tall, and the basement is very deep;
;; he will never find the top or bottom floors.
;;
;; For example:
;;
;; (()) and ()() both result in floor 0.
;; ((( and (()(()( both result in floor 3.
;; ))((((( also results in floor 3.
;; ()) and ))( both result in floor -1 (the first basement level).
;; ))) and )())()) both result in floor -3.
;;
;; To what floor do the instructions take Santa?
;; ---------------------------------------------------------------------
(defun parse-input (INPUT)
"Parse `INPUT' to determine where the instructions take Santa."
(let ((FLOOR-NUMBER 0))
(+ FLOOR-NUMBER (cond ((eql (first INPUT) nil) 0)
((eql (first INPUT) #\() (+ 1 (parse-input (rest INPUT))))
((eql (first INPUT) #\)) (- (parse-input (rest INPUT)) 1))))))
;; Test for correct answer
(assert (= 138 (parse-input *PUZZLE-INPUT*)))
;; I have elected to just throw this away and not do part 2 in this line of thinking.
;; Keeping it for posterity.
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