Scrabble game assistant: Given a set of letters, obtain the list of all possible words that can be formed with these letters or a subset of them. If possible, return words in longer-to-shorter order, as longer words provides more points for the player. This method would be used on a web-environment so it should be able to respond quickly to each request. For example, given the letters "HCAT" it should return: CHAT HAT CAT AT A