day18

2016/day18/input.rkt

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+#lang reader "lang.rkt"
+.^^^.^.^^^.^.......^^.^^^^.^^^^..^^^^^.^.^^^..^^.^.^^..^.^..^^...^.^^.^^^...^^.^.^^^..^^^^.....^....

2016/day18/lang.rkt

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+#lang br/quicklang ;; http://adventofcode.com/2016/day/18
+(provide read-syntax
+         (rename-out [mb #%module-begin]))
+
+(define (read-syntax path port)
+  (strip-bindings
+   #`(module mod "lang.rkt"
+       #,(string-trim (port->string port)))))
+
+(define-macro (mb STR)
+  #'(#%module-begin
+     (define (traps cs)
+       (length (filter (λ(c) (char=? #\. c)) cs)))
+     (let loop ([cs (string->list STR)]
+                [count (traps (string->list STR))]
+                [i 0])
+       (if (= i 399999) ; number of rows
+           count
+           (let* ([result (next-cs cs)]
+                  [this-count (traps result)])
+             (loop result (+ this-count count) (add1 i)))))))
+
+(define (next-cs cs)
+  (define adj-cs (append (list #\.) cs (list #\.)))
+  (for/list ([c1 (in-list adj-cs)]
+             [c2 (in-list (cdr adj-cs))]
+             [c3 (in-list (cddr adj-cs))])
+    (case (list c1 c2 c3)
+      [((#\^ #\^ #\.) (#\. #\^ #\^) (#\^ #\. #\.) (#\. #\. #\^)) #\^]
+      [else #\.])))

2016/day18/test.rkt

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+#lang reader "lang.rkt"
+.^^.^.^^^^