Ordered/ Unordered Dictionaries

[sapure]

Please, I'd like to know the difference and the special uses for each one.
If I want to use it for text file compression whose algorithm is as follows, which one is more efficient?

Encoding Algorithm
1. Initialize the dictionary to contain all blocks of length one (D={a,b}).
2. Search for the longest block W which has already appeared in the dictionary.
3. Encode W by its index (location) in the dictionary.
4. Add W followed by the first symbol of the next block to the dictionary.
5. If not done, go to (2).

Thanks, any help is appreciated.

[stultuske]

any help with what? where are you stuck?

[sapure]

I want to know ...

1) The difference between ordered & unordered dictionaries.
2) & Which type is more efficient for the previous algorithm.

Thanks.