finish day14

2016/day14/lang.rkt

@@ -1,7 +1,5 @@
-#lang br/quicklang
+#lang br/quicklang ;; http://adventofcode.com/2016/day/14
 (require openssl/md5)
-;; http://adventofcode.com/2016/day/13
-(require graph)
 (provide read-syntax
          (rename-out [mb #%module-begin]))
 
@@ -12,4 +10,32 @@
 
 (define-macro (mb SALT)
   #'(#%module-begin
-     (md5 (open-input-string SALT))))
+     (solve SALT)
+     (parameterize ([key-stretch 2017])
+       (solve SALT))))
+
+(define key-stretch (make-parameter 0))
+(require sugar/cache)
+(define/caching (get-hash salt i)
+  (for/fold ([str (string-downcase (format "~a~a" salt i))])
+            ([i (in-range (key-stretch))])
+    (md5 (open-input-string str))))
+
+(define (valid? hash salt i)
+  (let* ([triple-char-pat (pregexp "(.)\\1\\1")]
+         [result (regexp-match triple-char-pat hash)])
+    (and result
+         (let* ([repeated-char (cadr result)]
+                [penta-char-pat (pregexp (format "(~a)\\1\\1\\1\\1" repeated-char))])
+           (for/or ([idx (in-range (add1 i) (+ 1001 i))])
+             (regexp-match penta-char-pat (get-hash salt idx)))))))
+
+(define (solve salt)
+  (caar
+   (for/fold ([keys empty])
+             ([i (in-naturals)]
+              #:break (= (length keys) 64))
+     (define hash (get-hash salt i))
+     (if (valid? hash salt i)
+         (report* i hash (cons (cons i hash) keys))
+         keys))))