Advent of Code

I figure I would give it a try this year. Just some small problems to code out. I the language I chose to use was Common Lisp using sbcl. As of this post I just did Day 1 and Day 2. I’m using common lisp because I though it be fun to use and I still want to get better at using it. I still had to search around to find out how to use some of the functions in lisp still, but I feel I like I’m getting there.

Day 1

Day 1 was to find what 2 transactions summed equal to 2020 and give the product of those numbers (defparameter transactions nil) (defun read-file-in (filename) (with-open-file ( in filename :if-does-not-exist nil :external-format ‘(:utf-8 :replacement “?”)) (loop for line = ( read-line in nil nil ) while line collect line))) ;;part one (defun sum-2020? (transaction) (loop for item in transactions when (= (+ transaction item) 2020) return (* transaction item))) ;;part two (defun sum-three-2020? (transaction) (loop for item2 in transactions collect (loop for item3 in transactions when (= (+ transaction item2 item3) 2020) return (* transaction item2 item3))))

Day 2

Day 2’s was validating password rules from a database corruption. For this one I borrows a snippet from common lisp cookbook and rolled my own boolean-xor (defparameter password-policy nil) (defun read-file-in (filename) (with-open-file ( in filename :if-does-not-exist nil :external-format ‘(:utf-8 :replacement “?”)) (loop for line = ( read-line in nil nil ) while line collect line))) ;;took from http://cl-cookbook.sourceforge.net/strings.html (defun split-by-one-space (string) “Returns a list of substrings of string divided by ONE space each. Note: Two consecutive spaces will be seen as if there were an empty string between them.” (loop for i = 0 then (1+ j) as j = (position #\Space string :start i) collect (subseq string i j) while j)) (defun split-by-one-hypen (string) “returns a list of substrings of string divided by ONE hypen” (loop for i = 0 then (1+ j) as j = (position #- string :start i) collect (subseq string i j) while j)) (defun process-file-line (line) (list (car (split-by-one-hypen (car (split-by-one-space line)))) (car (cdr (split-by-one-hypen (car (split-by-one-space line))))) (subseq (car (cdr (split-by-one-space line))) 0 1) (car (cddr (split-by-one-space line))))) (defun boolean-xor ( test1 test2 ) (cond ((and test1 test2) nil) ((or test1 test2) t) (t nil))) (defun valid-password? (password) (if (<= (parse-integer (car password)) (count (char (caddr password) 0) (cadddr password) :test #‘equal) (parse-integer (cadr password))) t)) (defun valid-password2? (password) (if (boolean-xor (char= (char (caddr password) 0) (char (cadddr password) (- (parse-integer (car password)) 1))) (char= (char (caddr password) 0) (char (cadddr password) (- (parse-integer (cadr password)) 1)))) t)) (defun count-valid-passwords (pass-list) (loop for item in pass-list when item sum 1 into total finally (princ total)))