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1 files changed, 28 insertions, 0 deletions

diff --git a/racket/aoc2015/day-03/day-03.rkt b/racket/aoc2015/day-03/day-03.rkt
new file mode 100644
index 0000000..1d44955
--- /dev/null
+++ b/racket/aoc2015/day-03/day-03.rkt
@@ -0,0 +1,28 @@
+#lang racket
+(require "../../jj-aoc.rkt"
+         threading
+         (only-in algorithms chunks-of)
+         racket/hash)
+
+(define directions
+  (for/list ([l (in-input-port-chars (open-day 3 2015))])
+    (string->symbol (string l))))
+
+(define (trace-santa dirs)
+  (define visits (make-hash))
+  (for/fold ([x 0] [y 0] #:result visits) ([dir (in-list dirs)])
+    (hash-set! visits `(,x ,y) #true)
+    (match dir
+      ['^ (values x (add1 y))]
+      ['v (values x (sub1 y))]
+      ['< (values (add1 x) y)]
+      ['> (values (sub1 x) y)])))
+
+;; part 1
+(~> directions trace-santa hash-values length)
+
+;; part 2
+(~> directions (chunks-of 2) (apply map list _) (map trace-santa _) (match-define (list real robo) _))
+
+(hash-union! real robo #:combine (λ _ #true))
+(~> real hash-values length)