def Worker.sort(array, tmp, head, tail)
    #puts "GOT #{array.object_id} , #{head}, #{tail} : LEN = #{ tail-head} : #{tail-head > 0 }"
    if tail-head > 1
      mid = head +((tail-head) /2)
      #puts " 1 split TO #{head} - #{mid}"
      Worker.sort(array,tmp,  head, (mid))
      #puts " 2 split TO #{mid+1} - #{tail}"
      Worker.sort(array,tmp,  (mid+1), tail)
      #puts " 3 merge #{array.inspect}, #{head} #{mid} #{mid+1}, #{tail}"
      Worker.merge(array,tmp, head, mid, mid+1, tail)
    else
      #puts "Local switch"
      if array[head] > array[tail]
        array[head], array[tail] = array[tail], array[head]
      end
    end
  end


def Worker.merge(array, tmp_array, head1, tail1, head2, tail2)
    pr = head1
    p1 = head1

    tmp_array[head1..tail1] = array[head1..tail1]

    while p1 <= tail1 and head2 <= tail2
      if array[head2] > tmp_array[p1]
        array[pr] = tmp_array[p1]
        p1 +=1
      else
        array[pr] = array[head2]
        head2 +=1
      end
      #puts " PR #{pr}"
      pr += 1
    end

    diff = tail1 - p1
    array[pr..(pr+diff)] = tmp_array[p1..(p1+diff)] if diff >= 0

    #puts " |> #{ array.inspect}"
  end