d15

2017/d15/main.rkt

@@ -0,0 +1,28 @@
+#lang reader "../aoc-lang.rkt"
+(provide (rename-out [#%mb #%module-begin]) ★ ★★)
+
+(define-macro (#%mb (STARS) (Generator X starts with NUM) ...)
+  #`(#%module-begin
+     (apply STARS '(NUM ...))))
+
+(define (lower-16-bits x) (bitwise-bit-field x 0 16))
+
+(define (generator-base a b rounds [modulo-a 1] [modulo-b 1])
+  (for/fold ([a-last a]
+             [b-last b]
+             [sum 0]
+             #:result sum)
+            ([i (in-range rounds)])
+    (define a (for/fold ([a a-last])
+                        ([i (in-naturals)]
+                         #:break (and (positive? i) (zero? (modulo a modulo-a))))
+                (remainder (* 16807 a) 2147483647)))
+    (define b (for/fold ([b b-last])
+                        ([i (in-naturals)]
+                         #:break (and (positive? i) (zero? (modulo b modulo-b))))
+                (remainder (* 48271 b) 2147483647)))
+    (values a b (+ sum (if (= (lower-16-bits a) (lower-16-bits b)) 1 0)))))
+
+(define (★ a-start b-start) (generator-base a-start b-start 40000000))
+
+(define (★★ a-start b-start) (generator-base a-start b-start 5000000 4 8))

2017/d15/star1.rkt

@@ -0,0 +1,3 @@
+#lang reader "main.rkt" ★ ; 650
+Generator A starts with 783
+Generator B starts with 325

2017/d15/star2.rkt

@@ -0,0 +1,3 @@
+#lang reader "main.rkt" ★★
+Generator A starts with 783
+Generator B starts with 325

2017/d15/test1.rkt

@@ -0,0 +1,3 @@
+#lang reader "main.rkt" ★ ; 588
+Generator A starts with 65
+Generator B starts with 8921

2017/d15/test2.rkt

@@ -0,0 +1,3 @@
+#lang reader "main.rkt" ★★ ; 309
+Generator A starts with 65
+Generator B starts with 8921