Data commit

Task/LZW-compression/Erlang/lzw-compression.erl

@@ -0,0 +1,57 @@
+-module(lzw).
+
+-export([test/0, encode/1, decode/1]).
+
+-import(lists, [reverse/1, reverse/2]).
+
+test() ->
+    Str = "TOBEORNOTTOBEORTOBEORNOT",
+    [84,79,66,69,79,82,78,79,84,256,258,260,265,259,261,263] =
+  encode(Str),
+    Str = decode(encode(Str)),
+    ok.
+
+encode(Str) ->
+    D = init(dict:new()),
+    encode(Str, D, 256, []).
+
+encode([H], D, _, Out) ->
+    Val = dict:fetch([H], D),
+    reverse([Val|Out]);
+encode([H|T], D, Free, Out) ->
+    Val = dict:fetch([H], D),
+    find_match(T, [H], Val, D, Free, Out).
+
+find_match([H|T], L, LastVal, D, Free, Out) ->
+    case dict:find([H|L], D) of
+  {ok, Val} ->
+      find_match(T, [H|L], Val, D, Free, Out);
+  error ->
+      D1 = dict:store([H|L], Free, D),
+      encode([H|T], D1, Free+1, [LastVal|Out])
+    end;
+find_match([], _, LastVal, _, _, Out) ->
+    reverse([LastVal|Out]).
+
+decode([H|T]) ->
+    D   = init1(dict:new()),
+    Val = dict:fetch(H, D),
+    decode(T, Val, 256, D, Val).
+
+decode([], _, _, _, L) ->
+    reverse(L);
+decode([H|T], Old, Free, D, L) ->
+    Val = dict:fetch(H, D),
+    Add = [lists:last(Val)|Old],
+    D1  = dict:store(Free, Add, D),
+    decode(T, Val, Free+1, D1, Val ++ L).
+
+init(D) -> init(255, D).
+
+init(0, D) ->  D;
+init(N, D) ->  D1 = dict:store([N],N,D),  init(N-1, D1).
+
+init1(D) -> init1(255, D).
+
+init1(0, D) ->  D;
+init1(N, D) ->  D1 = dict:store(N,[N],D),  init1(N-1, D1).