Another update from ingydotnet^djgoku

Task/Longest-common-subsequence/Elixir/longest-common-subsequence.elixir

@@ -0,0 +1,42 @@
+defmodule LCS do
+  def lcs_length(s,t) do
+    {l,_c} = lcs_length(s,t,Map.new)
+    l
+  end
+
+  defp lcs_length([],t,cache), do: {0,Dict.put(cache,{[],t},0)}
+  defp lcs_length(s,[],cache), do: {0,Dict.put(cache,{s,[]},0)}
+  defp lcs_length([h|st]=s,[h|tt]=t,cache) do
+    {l,c} = lcs_length(st,tt,cache)
+    {l+1,Dict.put(c,{s,t},l+1)}
+  end
+  defp lcs_length([_sh|st]=s,[_th|tt]=t,cache) do
+    if Dict.has_key?(cache,{s,t}) do
+      {Dict.get(cache,{s,t}),cache}
+    else
+      {l1,c1} = lcs_length(s,tt,cache)
+      {l2,c2} = lcs_length(st,t,c1)
+      l = Enum.max([l1,l2])
+      {l,Dict.put(c2,{s,t},l)}
+    end
+  end
+
+  def lcs(s,t) do
+    {_,c} = lcs_length(s,t,Map.new)
+    lcs(s,t,c,[])
+  end
+
+  defp lcs([],_,_,acc), do: Enum.reverse(acc)
+  defp lcs(_,[],_,acc), do: Enum.reverse(acc)
+  defp lcs([h|st],[h|tt],cache,acc), do: lcs(st,tt,cache,[h|acc])
+  defp lcs([_sh|st]=s,[_th|tt]=t,cache,acc) do
+    if Dict.get(cache,{s,tt}) > Dict.get(cache,{st,t}) do
+      lcs(s,tt,cache,acc)
+    else
+      lcs(st,t,cache,acc)
+    end
+  end
+end
+
+IO.puts LCS.lcs('thisisatest','testing123testing')
+IO.puts LCS.lcs('1234','1224533324')