2 files changed, 46 insertions(+), 0 deletions(-)

A day06.lisp
A input/day06.txt

@@ 0,0 1,44 @@
+(defpackage #:advent2021.day06
+  (:use #:cl #:alexandria #:cl-ppcre #:advent2021.util)
+  (:export #:solve-part-1 #:solve-part-2))
+
+(in-package #:advent2021.day06)
+
+
+
+(defparameter +input+
+  ;; array of # of fish in each state
+  (first (parse-lines
+           (lambda (line)
+             (loop :with fishes := (make-array 9)
+                   :for n :in (mapcar #'parse-integer (split "," line))
+                   :do (incf (aref fishes n))
+                   :finally (return fishes))))))
+
+(defun tick-fish (fish)
+  (rotatef (aref fish 0)
+           (aref fish 1)
+           (aref fish 2)
+           (aref fish 3)
+           (aref fish 4)
+           (aref fish 5)
+           (aref fish 6)
+           (aref fish 7)
+           (aref fish 8))
+  (incf (aref fish 6)
+        (aref fish 8)))
+
+(defun solve (generations)
+  (let ((fish (copy-array +input+)))
+    (dotimes (i generations)
+      (tick-fish fish))
+
+    ;; return total fish
+    (loop :for n :across fish
+          :sum n)))
+
+(defun solve-part-1 ()
+  (solve 80))
+
+(defun solve-part-2 ()
+  (solve 256))

@@ 0,0 1,2 @@
+1,3,4,1,5,2,1,1,1,1,5,1,5,1,1,1,1,3,1,1,1,1,1,1,1,2,1,5,1,1,1,1,1,4,4,1,1,4,1,1,2,3,1,5,1,4,1,2,4,1,1,1,1,1,1,1,1,2,5,3,3,5,1,1,1,1,4,1,1,3,1,1,1,2,3,4,1,1,5,1,1,1,1,1,2,1,3,1,3,1,2,5,1,1,1,1,5,1,5,5,1,1,1,1,3,4,4,4,1,5,1,1,4,4,1,1,1,1,3,1,1,1,1,1,1,3,2,1,4,1,1,4,1,5,5,1,2,2,1,5,4,2,1,1,5,1,5,1,3,1,1,1,1,1,4,1,2,1,1,5,1,1,4,1,4,5,3,5,5,1,2,1,1,1,1,1,3,5,1,2,1,2,1,3,1,1,1,1,1,4,5,4,1,3,3,1,1,1,1,1,1,1,1,1,5,1,1,1,5,1,1,4,1,5,2,4,1,1,1,2,1,1,4,4,1,2,1,1,1,1,5,3,1,1,1,1,4,1,4,1,1,1,1,1,1,3,1,1,2,1,1,1,1,1,2,1,1,1,1,1,1,1,2,1,1,1,1,1,1,4,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2,1,1,2,5,1,2,1,1,1,1,1,1,1,1,1
+