From 72cfb197248025c282124122c7f4ee306fe0f347 Mon Sep 17 00:00:00 2001
From: Matthew Butterick <mb@mbtype.com>
Date: Thu, 1 Dec 2016 12:33:46 -0800
Subject: [PATCH] not working

---
 2016/day01.rkt | 64 +++++++++++++++++++++++++++++++++++---------------
 1 file changed, 45 insertions(+), 19 deletions(-)

diff --git a/2016/day01.rkt b/2016/day01.rkt
index 705acd7..999d930 100644
--- a/2016/day01.rkt
+++ b/2016/day01.rkt
@@ -3,33 +3,59 @@
 (module+ reader
   (provide read-syntax)
   (define (read-syntax path port)
+    (define turn-strings (string-split (port->string port) ", "))
+    (define turn-pattern #px"^([LR])(\\d+)$")
+    (define turn-datums
+      (for*/list ([tstr (in-list turn-strings)])
+                 (define match-result (regexp-match turn-pattern (string-trim tstr)))
+                 `(turn ,@(cdr (or match-result empty)))))
     (strip-bindings
      #`(module day01-mod "day01.rkt"
-         #,@(for/list ([t (in-list (string-split (port->string port) ", "))])
-                      `(turn ,@(string-split (string-trim t) #px"(?<=[LR])")))))))
+         #,@turn-datums))))
 
 (define-macro (mb . TURNS)
   #'(#%module-begin
      (solve . TURNS)))
 (provide (rename-out [mb #%module-begin]))
 
-(define (solve . turns)
-  (define loc
-    (let loop ([loc 0]
-               [dir 1]
-               [turns turns])
-      (if (empty? turns)
-          loc
-          (let* ([turn (car turns)]
-                 [rotation (car turn)]
-                 [dist (cdr turn)]
-                 [new-dir (* dir rotation)])
-            (loop (+ loc (* new-dir dist)) new-dir (cdr turns))))))
+(define (loc-dist loc)
   (+ (abs (imag-part loc)) (abs (real-part loc))))
 
-(define-macro (turn DIR DIST)
-  (with-pattern ([NEW-DIR (syntax-case #'DIR ()
-                            ["L" #'+i]
-                            ["R" #'-i])])
-    #'(cons NEW-DIR (string->number DIST))))
+(define (locs-between loca locb)
+  (range loca (add1 locb)))
+
+(module+ test
+  (require rackunit)
+  (check-equal? (locs-between 0 3) '(0 1 2 3))
+  (check-equal? (locs-between 3 0) (reverse (locs-between 0 3)))
+  (check-equal? (locs-between +0i +3i) '(+0i +1i +2i +3i))
+  (check-equal? (locs-between +3i +0i) (reverse (locs-between +0i +3i))))
+
+(define (solve . turns)
+  (define first-loc-visited-twice #f)
+  (define north 0+1i)
+  (let loop ([locs (list 0+0i)] [dir north] [turns turns])
+    (if (empty? turns)
+        (displayln (format "part 1 (dist of final location): ~a" (loc-dist (car locs))))
+        (let* ([turn (car turns)]
+               [rotation (car turn)]
+               [new-dir (* dir rotation)]
+               [dist (cdr turn)]
+               [loc (car locs)]
+               [new-loc (+ loc (* new-dir dist))])
+          
+          (when (and
+                 (not first-loc-visited-twice)
+                 (report* locs loc new-loc (member new-loc locs)))
+            (set! first-loc-visited-twice new-loc)
+            (displayln (format "part 2 (dist of first twice-visited location): ~a" (loc-dist new-loc))))        
+          (loop (report (append (locs-between new-loc loc) (cdr locs))) new-dir (cdr turns))))))
+
+(define-macro-cases turn
+  [(_ DIR DIST)
+   (with-pattern ([NEW-DIR (syntax-case #'DIR ()
+                             ["L" #'+i]
+                             ["R" #'-i])])
+     #'(cons NEW-DIR (string->number DIST)))]
+  [else #'(void)])
 (provide turn)
\ No newline at end of file