find_info(File) ->
    case file:read_file_info(File) of
        {ok, Facts} ->
            case Facts#file_info.type of
                directory -> directory;
                regular -> regular
            end;
        {error,Reason} -> exit(Reason)
    end.

find_files(Dir,Flag,Ending,Acc) ->
    case file:list_dir(Dir) of
        {ok,A} -> find_files_helper(A,Dir,Flag,Acc,Ending);
        {_,_} -> Acc
    end.

find_files_helper([H|Tail],Dir,Flag,Acc,Ending) ->
    A = find_info(filename:absname_join(Dir,H)),
    case A of
        directory ->
            case Flag of
                true ->
                    find_files(filename:absname_join(Dir,H),Flag,Ending,Acc ++ find_files_helper(Tail,Dir,Flag,Acc,Ending));
                false -> find_files_helper(Tail,Dir,Flag,Acc,Ending)
            end;
        regular ->
        case filename:extension(H) of
            Ending -> find_files_helper(Tail,Dir,Flag,[to_md5_large(H)] ++ Acc, Ending);
            _ -> find_files_helper(Tail,Dir,Flag,Acc,Ending)
        end;
        {error,Reason} -> exit(Reason)
    end;
find_files_helper([],_,_,Acc,_) -> Acc.

home/
   a/
     ser.erl
   b/
   c/
file.erl
file2.erl

home/
   a/
     ser.erl
     back.erl
   b/
   c/
file.erl
file2.erl