6

6/fish.lisp

@@ -0,0 +1,40 @@
+(defparameter *fish-input* "./input.txt")
+(ql:quickload :cl-strings)
+(use-package :cl-strings)
+
+(defun read-fish ()
+  "Read input file, returning a list of its fish ages."
+  (let ((input (open *fish-input* :if-does-not-exist nil))
+        (fish-ages '()))
+    (when input
+      (setq fish-ages (map 'list 'parse-integer (cl-strings:split (read-line input nil) ",")))
+      (close input))
+
+    fish-ages))
+
+(defun process-fish (input-fish)
+  (defun fish-iter (fish new-fish-ages new-fish-count)
+    (if (eq fish '())
+        (append new-fish-ages
+                (loop for x upto (1- new-fish-count) collect 8))
+        (let ((current-fish (car fish)))
+          (cond ((= current-fish 0)
+                 (fish-iter (cdr fish) (cons 6 new-fish-ages) (1+ new-fish-count)))
+                ('true
+                 (fish-iter (cdr fish) (cons (1- current-fish) new-fish-ages) new-fish-count))))))
+
+  (reverse (fish-iter input-fish '() 0)))
+
+(defun process-fish-generations (generations fish)
+  (defun my-fish-iter (gens fish-ages)
+    (if (= gens 0)
+        fish-ages
+        (my-fish-iter (1- gens) (process-fish fish-ages))))
+  (my-fish-iter generations fish))
+
+(length (process-fish-generations 80 (read-fish)))
+;; -> 352872
+
+;; Part 2: 256 generations
+;;  my solution is too naive to process this many generations
+;;  efficiently :/

6/input.txt

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