day6

day6.rkt

@@ -0,0 +1,76 @@
+#lang racket
+
+(define (tick fishes)
+  (foldl (λ (fish lst)
+           (if (= fish 0)
+               (cons 6 (cons 8 lst))
+               (cons (sub1 fish) lst))) '() fishes))
+
+(define (generations fishes num)
+  (if (= num 0)
+      fishes
+      (generations (tick fishes) (sub1 num))))
+
+(define part1
+  (let* ([line (first (file->lines "day6.txt"))]
+         [fishes (map string->number (string-split line ","))])
+        (length (generations fishes 80))))
+
+part1
+
+; part2
+
+(define (memo2 fn arg1 arg2)
+  (let* ([ht (make-hash)])
+    (hash-ref! ht (list fn arg1 arg2) (fn arg1 arg2))))
+
+(define/match (count-one digit time-left)
+  [(n 0) 1]
+  [(0 t) (+ (count-one 6 (sub1 t)) (count-one 8 (sub1 t)))]
+  [(n t) (count-one (sub1 n) (sub1 t))])
+
+(define count-one-memo (λ (x y) (memo2 count-one x y)))
+
+(define part2-slow
+  (let* ([line (first (file->lines "day6.txt"))]
+         [fishes (map string->number (string-split line ","))])
+    (foldl (λ (x acc) (+ acc (count-one-memo x 100))) 0 fishes)))
+
+; okay so memoing didn't help. ahhh i know what to do
+
+(define (tick2 ht)
+  (define temp (hash-copy ht))
+  (hash-set! ht 0 (hash-ref temp 1 0))
+  (hash-set! ht 1 (hash-ref temp 2 0))
+  (hash-set! ht 2 (hash-ref temp 3 0))
+  (hash-set! ht 3 (hash-ref temp 4 0))
+  (hash-set! ht 4 (hash-ref temp 5 0))
+  (hash-set! ht 5 (hash-ref temp 6 0))
+  (hash-set! ht 6 (+ (hash-ref temp 0 0) (hash-ref temp 7 0)))
+  (hash-set! ht 7 (hash-ref temp 8 0))
+  (hash-set! ht 8 (hash-ref temp 0 0)))
+
+(define (add-num ht num)
+  (hash-set! ht num (+ 1 (hash-ref ht num 0))))
+
+(define (init ht nums)
+  (for ([num (in-list nums)])
+    (add-num ht num)))
+
+(define (loop ht max)
+  (if (= 0 max)
+      ht
+      (begin
+        (tick2 ht)
+        (loop ht (sub1 max)))))
+
+(define part2
+  (let* ([line (first (file->lines "day6.txt"))]
+         [fishes (map string->number (string-split line ","))]
+         [ht (make-hash)])
+    (begin
+     (init ht fishes)
+     (loop ht 256)
+     (foldl + 0 (hash-values ht)))))
+
+part2

day6.test.txt

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

day6.txt

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