tasks a-s

Task/Run-length-encoding/Erlang/run-length-encoding.erl

@@ -0,0 +1,46 @@
+-module(rle).
+
+-export([encode/1,decode/1]).
+
+-include_lib("eunit/include/eunit.hrl").
+
+encode(S) ->
+    doEncode(string:substr(S, 2), string:substr(S, 1, 1), 1, []).
+
+doEncode([], CurrChar, Count, R) ->
+    R ++ integer_to_list(Count) ++ CurrChar;
+doEncode(S, CurrChar, Count, R) ->
+    NextChar = string:substr(S, 1, 1),
+    if
+        NextChar == CurrChar ->
+            doEncode(string:substr(S, 2), CurrChar, Count + 1, R);
+        true ->
+            doEncode(string:substr(S, 2), NextChar, 1,
+                R ++ integer_to_list(Count) ++ CurrChar)
+    end.
+
+decode(S) ->
+    doDecode(string:substr(S, 2), string:substr(S, 1, 1), []).
+
+doDecode([], _, R) ->
+    R;
+doDecode(S, CurrString, R) ->
+    NextChar = string:substr(S, 1, 1),
+    IsInt = erlang:is_integer(catch(erlang:list_to_integer(NextChar))),
+    if
+        IsInt ->
+            doDecode(string:substr(S, 2), CurrString ++ NextChar, R);
+        true ->
+            doDecode(string:substr(S, 2), [],
+                R ++ string:copies(NextChar, list_to_integer(CurrString)))
+    end.
+
+rle_test_() ->
+    PreEncoded =
+        "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW",
+    Expected = "12W1B12W3B24W1B14W",
+    [
+        ?_assert(encode(PreEncoded) =:= Expected),
+        ?_assert(decode(Expected) =:= PreEncoded),
+        ?_assert(decode(encode(PreEncoded)) =:= PreEncoded)
+    ].