diff --git a/2016/day05.rkt b/2016/day05.rkt
index 3668599..b25d605 100644
--- a/2016/day05.rkt
+++ b/2016/day05.rkt
@@ -4,22 +4,38 @@
 (define (read-syntax path port)
   (strip-bindings
    #`(module mod "day05.rkt"
-       (solve-part-a #,(string-trim (port->string port))))))
+       (solve #,(string-trim (port->string port))))))
 (module+ reader (provide read-syntax))
 
 (provide #%module-begin)
 
-(define (solve-part-a key)
-  (display "part a solution: ")
-  (for*/fold ([password-cs empty])
-            ([idx (in-naturals)]
-             [this-key (in-value (format "~a~a" key idx))]
-             #:break (= 8 (length password-cs)))
-    (define this-hash (md5 (open-input-string this-key)))
-    (if (string-prefix? this-hash "00000")
-        (let ([next-str (substring this-hash 5 6)])
-          (display next-str)
-          (cons next-str password-cs))
-        password-cs))
-  (displayln ""))
-(provide solve-part-a)
+(define (solve key)
+  (define-values
+    (part-a-solution part-b-solution)
+    (for*/fold ([part-a empty]
+                [part-b (make-vector 8 #f)])
+               ([idx (in-naturals 1000000)]
+                [this-key (in-value (format "~a~a" key idx))]
+                #:break (and (= 8 (length part-a))
+                             (andmap string? (vector->list part-b))))
+      (define this-hash (md5 (open-input-string this-key)))
+      (define next-part-a
+        (if (and (not (= 8 (length part-a)))
+                 (string-prefix? this-hash "00000"))
+            (let ([next-str (substring this-hash 5 6)])
+              (displayln (format "part a progress: ~a" next-str))
+              (cons next-str part-a))
+            part-a))
+      (define next-part-b
+        (let ()
+          (when (and (string-prefix? this-hash "00000")
+                     (string->number (substring this-hash 5 6))
+                     (<= 0 (string->number (substring this-hash 5 6)) 7)
+                     (not (vector-ref part-b (string->number (substring this-hash 5 6)))))
+            (displayln (format "part b progress: idx ~a, hash ~a, ~a at ~a" idx this-hash (substring this-hash 6 7) (substring this-hash 5 6)))
+            (vector-set! part-b (string->number (substring this-hash 5 6)) (substring this-hash 6 7)))
+          part-b))
+      (values next-part-a next-part-b)))
+  (displayln (format "part a: ~a" (apply string-append (reverse part-a-solution))))
+  (displayln (format "part b: ~a" (apply string-append (vector->list part-b-solution)))))
+(provide solve)