initial commit

1 files changed, 23 insertions, 0 deletions

diff --git a/2021/day1/01b.rkt b/2021/day1/01b.rkt
new file mode 100644
index 0000000..40337a4
--- /dev/null
+++ b/2021/day1/01b.rkt
@@ -0,0 +1,23 @@
+#lang racket
+(require threading)
+
+(define input (file->lines "input"))
+
+(define (map-differing-lengths f . arrs)
+  (define minLength (apply min (map length arrs)))
+  (define newLists (map (lambda (x) (take x minLength)) arrs))
+  (apply map (cons f newLists)))
+
+(define (build-windows xs)
+  (map-differing-lengths list xs (cdr xs) (drop xs 2)))
+
+(define (diff-pairs xs)
+  (map-differing-lengths - (cdr xs) xs))
+
+(~>> input
+    (map string->number)
+    (build-windows)
+    (map (lambda (x) (apply + x)))
+    (diff-pairs)
+    (filter positive?)
+    (length _))