rookNumber -- Rook number of a collection of cells
Usage:
rookNumber(Q)
Inputs:
Q, a collection of cells
Outputs:
the maximum number of rooks that can be placed on Q in non-attacking positions.
Description
Given a collection of cells $\mathcal{P}$, this routine computes the maximum number of rooks that can be placed on $\mathcal{P}$ in non-attacking position.