ADDED   day01.rkt
Index: day01.rkt
==================================================================
--- day01.rkt
+++ day01.rkt
@@ -0,0 +1,36 @@
+#lang racket
+(require rackunit)
+
+(define input (file->lines "day01-input.txt"))
+
+(define start-frequency 0)
+
+(define (day01-part1)
+  (apply + start-frequency (map string->number input)))
+
+(module+ test
+  (check-equal? (day01-part1) 486)) ; Correct answer for part1
+
+(define (day01-part2 [freq-changes (map string->number input)]
+                     [start-from start-frequency]
+                     [seen-frequencies (list start-frequency)])
+  (define run-through
+    (for/fold ([seen seen-frequencies]
+               [current-freq start-from]
+               #:result seen)
+              ([freq-change (in-list freq-changes)])
+      #:final (member (+ current-freq freq-change) seen)
+      (values (append seen (list (+ current-freq freq-change))) (+ current-freq freq-change))))
+  (cond
+    [(check-duplicates run-through)
+     (last run-through)]
+    [else
+     (day01-part2 freq-changes (last run-through) run-through)]))
+
+(module+ test
+  (check-equal? (day01-part2 '(3 3 4 -2 -4)) 10)
+  (check-equal? (day01-part2 '(-6 3 8 5 -6)) 5)
+  (check-equal? (day01-part2 '(7 7 -2 -7 -4)) 14)
+  ; Actually getting the correct answer for my input takes a really long time
+  ; (check-equal? (day01-part2) 69285)
+  )