Yet Another Novice Tries To Write AGo Program/ Move Undo Data Structure And Algorithm

I gleaned this from Bruce Wilcox's discussion of RiscIgo. He describes his move structure as:

• Color (1 bit)
• Location (9 bits)
• Ko Flag (1 bit)
• Kill Directions (4 bits)
• Plus 1 unused bit = 16 bits

What caught my eye is Kill Directions. How can 4 bits be enough information to replace captured stones upon undo? Ah, well of course! You just flood fill starting at the adjacent empty point(s).

Capture  

is:

• Color: White
• Location:
• Ko:no
• Kill Directions: North (or East), South

Undo  

To undo this move, just flood fill with opposite color from the North (n) and South (s) points and then empty the location.

Undo  

Nifty!