What is the least number of white knights that can be placed on a standard chessboard so that a black piece cannot be added to an unoccupied square without being under attack?

An 8 x 8 chessboard has 64 fields.  A knight can attack 8 fields max and occupies 1 field, so one knight = 9 fields.
The corner field (A1 types) need a knight at one jump away.  this knight looses two fields it's covering and attacks max 6 fields.
We have 4 x 6 fields under attack, leaving 64-24-4(Occupied fields) = 36 free fields.
To cover the free fields we need 4 more knights.
Total minimum 8 knights.

Posted by Hugo on 2005-01-26 20:25:43