day04

1 files changed, 31 insertions, 0 deletions

diff --git a/day04.rkt b/day04.rkt
new file mode 100644
index 0000000..4f9ba21
--- /dev/null
+++ b/day04.rkt
@@ -0,0 +1,31 @@
+#lang racket
+(require (for-syntax syntax/for-body)
+         syntax/parse/define)
+
+(define-syntax-parse-rule (for/count clauses body ... tail-expr)
+  #:with original this-syntax
+  #:with ((pre-body ...) (post-body ...))
+         (split-for-body this-syntax #'(body ... tail-expr))
+  (for/fold/derived original
+    ([count 0])
+    clauses
+    pre-body ...
+    (define maybe-count (let () post-body ...))
+    (if maybe-count
+      (+ count 1)
+      count)))
+
+
+(for/count ([line (file->lines "day04")])
+  (match-let ([(list a b c d) (map string->number
+                                   (string-split line #px"[^0-9]"))])
+    (or (<= a c d b)
+        (<= c a b d))))
+; 651
+
+(for/count ([line (file->lines "day04")])
+  (match-let ([(list a b c d) (map string->number
+                                   (string-split line #px"[^0-9]"))])
+    (and (<= c b)
+         (<= a d))))
+; 956