a ring of squares
A ring of N squares, the N is a multiple of 3.
"K" squares in the ring are painted of white, and the other squares are painted black. We have a SWITCH operator, that turns the color of 3 adjacent squares in the ring, (black to white / white to black).
We want to turn all the squares in the ring to white. For which values of K (relative to N) can the goal be achieved? ?