tasks a-s

Task/Run-length-encoding/Standard-ML/run-length-encoding.ml

@@ -0,0 +1,17 @@
+fun encode str =
+  let
+    fun aux (sub, acc) =
+      case Substring.getc sub
+       of NONE           => rev acc
+        | SOME (x, sub') =>
+            let
+              val (y, z) = Substring.splitl (fn c => c = x) sub'
+            in
+              aux (z, (x, Substring.size y + 1) :: acc)
+            end
+  in
+    aux (Substring.full str, [])
+  end
+
+fun decode lst =
+  concat (map (fn (c,n) => implode (List.tabulate (n, fn _ => c))) lst)