Data commit

Task/Longest-common-substring/Racket/longest-common-substring.rkt

@@ -0,0 +1,25 @@
+#lang typed/racket
+(: lcs (String String -> String))
+(define (lcs a b)
+  (: all-substrings# (String -> (HashTable String Boolean)))
+  (define (all-substrings# str)
+    (define l (string-length str))
+    (for*/hash : (HashTable String Boolean)
+      ((s (in-range 0 l)) (e (in-range (add1 s) (add1 l))))
+      (values (substring str s e) #t)))
+
+  (define a# (all-substrings# a))
+
+  (define b# (all-substrings# b))
+
+  (define-values (s l)
+    (for/fold : (Values String Nonnegative-Integer)
+    ((s "") (l : Nonnegative-Integer 0))
+    ((a_ (in-hash-keys a#))
+     #:when (and (> (string-length a_) l) (hash-ref b# a_ #f)))
+    (values a_ (string-length a_))))
+
+  s)
+
+(module+ test
+  ("thisisatest" . lcs . "testing123testing"))