Welcome

No problem. Ahh, well as a note, DrussGT is not the easiest surfer to read IMO.

Hmm.. for the questions:

1) A kd-tree is a data structure used to do a "k-nearest-neighbor" search fast. What the "k-nearest-neighbor" search does, is it allows you to search a history for the past situations most similar to the current situation. You give numeric values to different aspects of the situation,

2a) To save between rounds, you just use a "static" variable in Java. The "static" keyword makes it so the value is is common between all instances of a class, such as between separate rounds. Basically all bots that learn use this.

2b) To store between matches you need to use some robocode APIs for writing and reading files. I don't like using it because it makes a bot rank more favorably in the rumble if fewer clients are running at a time, due to learned information being separate between each client. Note that LittleBlackBook is different because it only reads this way, because it's whole strategy is having a pre-written data file. I would also note that relatively few robots use cross-round data saving.

3) Well... my first robot was a weird multi-mode thing that took several weeks to make, but I never released it. The first bot I ever released was LunarTwins. For LunarTwins it took 24 hours for "the inspiration to ferment", and the first released version of the code was finished within a 36 hour period of time. Really though, LunarTwins was fast to write because it's a non-learning robot. My second publicly released robot was RougeDC which was my first surfer. I don't remember how long that bot took, but I know I spent most of Summer 2008 working on various versions of it.