refactor isSublist

exercism · Jan 3, 2024 · 8b518e2 · 8b518e2
1 parent f3db258
commit 8b518e2
Showing 1 changed file with 7 additions and 3 deletions.
diff --git a/exercises/practice/sublist/.meta/example.sml b/exercises/practice/sublist/.meta/example.sml
@@ -5,10 +5,14 @@ datatype relation =
   | Unequal
 
 local
+  fun isPrefix (listOne: int list, listTwo: int list): bool =
+    case (listOne, listTwo) of
+        (nil, _) => true
+      | (_, nil) => false
+      | (firstOne :: restOne, firstTwo :: restTwo) => firstOne = firstTwo andalso isPrefix (restOne, restTwo)
+
   fun isSublist (listOne: int list, listTwo: int list): bool =
-    if length listTwo < length listOne then false
-    else if listOne = List.take (listTwo, length listOne) then true
-    else isSublist (listOne, tl listTwo)
+    isPrefix (listOne, listTwo) orelse (listTwo <> nil andalso isSublist (listOne, tl listTwo))
 in
   fun sublist (listOne: int list, listTwo: int list): relation =
     if listOne = listTwo then Equal