a) The minimum number of counters that need be placed on a nxn chessboard such that no additional counters can be placed without creating any straight line of 3;

b) The maximum number of counters that can be placed on a nxn chessboard such that no three lie in a straight line.

Remember that positions like A1, B3, and C5 are in a straight line.
(Try to continue the sequences if you can)

Turns out that for a 7x7 grid, part (a) can be accomplished with only 10 markers.  Still don't know if that's the minimum, although I suspect that it is.  I haven't checked to see if there are better solutions for the others yet...

Posted by tomarken on 2006-04-26 16:43:35