pain

data/day6.txt

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

day6.rkt

@@ -0,0 +1,98 @@
+#lang racket
+(require "lib/common.rkt"
+         fancy-app)
+
+(define (generate-initial-hash fish)
+  (define res (make-hash))
+  (for ([f (in-list fish)])
+    (hash-update! res f add1 0))
+  res)
+
+(define (simulate-day! hsh)
+  (define copy (hash-copy hsh))
+  (for ([(f k) (in-hash copy)])
+    (cond [(zero? f)
+           ;; add k 8s
+           (hash-update! hsh 8 (+ k _) 0)
+           ;; add k 6s
+           (hash-update! hsh 6 (+ k _) 0)
+           ;; reset zero
+           (hash-set! hsh 0 0)]
+          [else
+           ;; move it down
+           (hash-update! hsh (- f 1) (+ k _) 0)
+           (hash-update! hsh f (- _ k) 0)])))
+
+(define (day6a fish)
+  (define count-hash (generate-initial-hash fish))
+
+  (for ([_ (in-range 80)])
+    (simulate-day! count-hash))
+
+  (foldl + 0 (hash-values count-hash)))
+
+(define (day6b fish)
+  (define count-hash (generate-initial-hash fish))
+
+  (for ([_ (in-range 256)])
+    (simulate-day! count-hash))
+
+  (foldl + 0 (hash-values count-hash)))
+
+(module+ main
+  (call-with-input-file "data/day6.txt"
+    (λ (prt)
+      (define fish
+        (~> (port->string prt)
+            string-split
+            first
+            (string-split ",")
+            (map string->number _)))
+      (answer 6 1 (day6a fish))
+      (answer 6 2 (day6b fish)))))
+
+(module+ test
+  (require rackunit)
+  (define test-fish '(3 4 3 1 2))
+  (define init-hash (generate-initial-hash test-fish))
+  (check-equal? (hash->list init-hash)
+                (hash->list (hash 1 1
+                                  2 1
+                                  3 2
+                                  4 1)))
+  (simulate-day! init-hash)
+  (check-equal? (sort #:key car (hash->list init-hash) <)
+                (sort #:key car
+                      (hash->list (hash 0 1
+                                        1 1
+                                        2 2
+                                        3 1
+                                        4 0))
+                      <))
+  (simulate-day! init-hash)
+  (check-equal? (sort #:key car (hash->list init-hash) <)
+                (sort #:key car
+                      (hash->list (hash 0 1
+                                        1 2
+                                        2 1
+                                        3 0
+                                        4 0
+                                        6 1
+                                        8 1))
+                      <))
+  (simulate-day! init-hash)
+  (check-equal? (sort #:key car (hash->list init-hash) <)
+                (sort #:key car
+                      (hash->list (hash 0 2
+                                        1 1
+                                        2 0
+                                        3 0
+                                        4 0
+                                        5 1
+                                        6 1
+                                        7 1
+                                        8 1))
+                      <))
+
+  (check-equal? (day6a test-fish) 5934)
+  (check-equal? (day6b test-fish) 26984457539))

tmpl.rkt

@@ -9,7 +9,7 @@
 
 (module+ main
   (call-with-input-file "data/dayN.txt"
-    (lambda (prt)
+    (λ (prt)
       (define lines (port->lines prt))
       (answer N 1 (dayNa lines))
       (answer N 2 (dayNb lines)))))