These 2 days, I'm trying to code some standard iimplementation out. Dun expect that when it's standard implementation, it would be easy. It's totally beyond one can imagine. You just can't map the thing you are coding to a concrete thing in life. The data structure is something that cannot does not exist within our imagination. I really had a hard time coding and debugging. Can say now its about 70% finsihed, with only one simple test case. Mr BLOG