Day 14

Added solution for day 14. Nice exercise for vectors with fillpointers.

advent-of-code-2018.asd

@@ -21,4 +21,5 @@
                (:file "day10")
                (:file "day11")
                (:file "day12")
-               (:file "day13")))
+               (:file "day13")
+               (:file "day14")))

day14.lisp

@@ -0,0 +1,49 @@
+;;;; day14.lisp
+
+(in-package :advent-of-code-2018)
+
+(defun day14-prepare-recipes (length)
+  (let ((recipes
+          (make-array (+ length 10) :fill-pointer 0
+                                    :element-type '(mod 10)
+                                    :adjustable t)))
+    (vector-push 3 recipes)
+    (vector-push 7 recipes)
+    recipes))
+
+(defun day14-digits (number)
+  (nreverse (loop
+              :for (rest digit) := (multiple-value-list (floor number 10))
+              :then (multiple-value-list (floor rest 10))
+              :collect digit
+              :while (> rest 0))))
+
+(defun day14 (&optional (input 327901))
+  (loop :with recipes := (day14-prepare-recipes input)
+        :for elf1 := 0 :then (mod (+ elf1 1 recipe1) (length recipes))
+        :for elf2 := 1 :then (mod (+ elf2 1 recipe2) (length recipes))
+        :for recipe1 := (aref recipes elf1)
+        :for recipe2 := (aref recipes elf2)
+        :do (dolist (new-recipe (day14-digits (+ recipe1 recipe2)))
+              (vector-push new-recipe recipes))
+        :while (< (length recipes) (array-dimension recipes 0))
+        :finally (format t "Answer Part1: ~a~%"
+                         (map 'string #'digit-char (subseq recipes input)))))
+
+(defun day14-extra (&optional (input 327901))
+  (loop :with recipes := (day14-prepare-recipes 21000000)
+        :with code := (day14-digits input)
+        :with at := 0
+        :for elf1 := 0 :then (mod (+ elf1 1 recipe1) (length recipes))
+        :for elf2 := 1 :then (mod (+ elf2 1 recipe2) (length recipes))
+        :for recipe1 := (aref recipes elf1)
+        :for recipe2 := (aref recipes elf2)
+        :do (dolist (new-recipe (day14-digits (+ recipe1 recipe2)))
+              (vector-push-extend new-recipe recipes 10000)
+              (cond
+                ((null (nth at code)) (incf at))
+                ((eql (nth at code) new-recipe) (incf at))
+                (t (setf at 0))))
+        :while (nth at code)
+        :finally (format t "Answer Part2: ~a~%"
+                         (- (length recipes) at))))