aoc21/aoc21.lisp

;;; Day 1

(defun read-1 (file)
  (with-open-file (stream file)
    (loop for line = (read-line stream nil)
	  while line
	  collect (parse-integer line))))

(defun solve-1-1 (file)
  (let ((readings (read-1 file))
	(inc-acc 0))
    (labels ((rec (list old)
	       (if list
		   (progn
		     (if (< old (first list))
			 (incf inc-acc))
		     (rec (cdr list) (first list))))))
      (rec (cdr readings) (first readings))
      inc-acc)))

(defun solve-1-2 (file)
  (let ((readings (read-1 file))
	(inc-acc 0))
    (labels ((rec (list old-sum)
	       (if (cddr list)
		   (let ((sum (reduce #'+ (subseq list 0 3))))
		     (if (< old-sum sum)
			 (incf inc-acc))
		     (rec (cdr list) sum)))))
      (rec (cdr readings) (reduce #'+ (subseq readings 0 3)))
      inc-acc)))

;;; Day 2

(defun setup-solution-2 (stage)
  (let ((position (vector 0 0))
	(aim 0))
    (defun forward (n)
      (incf (elt position 0) n)
      (if (= stage 2) (incf (elt position 1) (* n aim))))
    (defun up (n)
      (if (= stage 1)
	  (decf (elt position 1) n)
	  (decf aim n)))
    (defun down (n)
      (if (= stage 1)
	  (incf (elt position 1) n)
	  (incf aim n)))
    (defun zero ()
      (setf position (vector 0 0) aim 0))
    (defun result ()
      position)))

(defun read-2-1 (file)
  (with-open-file (stream file)
    (loop for line = (read-line stream nil)
	  while line
	  collect (multiple-value-bind (symbol length) (read-from-string line)
		    (list symbol (parse-integer (subseq line length)))))))

(defun solve-2-1 (data)
  (setup-solution-2 1)
  (eval (cons 'progn data))
  (reduce #'* (result)))

(defun solve-2-2 (data)
  (setup-solution-2 2)
  (eval (cons 'progn data))
  (reduce #'* (result)))