codewars: solve 'consecutive strings' challenge

codewars/ocaml/rank-up/consecutive-strings/main.ml

@@ -0,0 +1,15 @@
+let rec takeFirstN (xs : string list) (n : int) (acc : string) : string =
+    match n with
+    | 0 -> acc
+    | x -> takeFirstN (List.tl xs) (n-1) (acc ^ (List.nth xs 0));;
+
+let rec joinK (xs : string list) (acc : string list) (k : int) : string list =
+  if List.length xs < k then acc
+  else joinK (List.tl xs) (acc @ [takeFirstN xs k ""]) k;;
+
+let longestConsec (xs : string list) (k : int) : string =
+  if (List.length xs) == 0 || (List.length xs) < k || k <= 0
+  then ""
+  else
+    let pairs = joinK xs [] k in
+    List.fold_left (fun acc i -> if (String.length i) > (String.length acc) then i else acc) "" pairs;;