How to compute ROOK Polynomials for NxM Matrices [closed]

How to compute ROOK Polynomials for NxM Matrices for k objects ?

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closed as off topic by Karolina Sołtys, Aaron Sterling, Lev Reyzin♦, Kaveh, Peter Shor Nov 3 '10 at 3:35

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Tuhin, the purpose of this site is not for asisting in homework. I'd say you may look at stackoverflow.com, but you already asked there (stackoverflow.com/questions/4071804/matrix-problem-in-c) – Diego de Estrada Nov 3 '10 at 1:44
Also, "rook" shouldn't be capitalized. It's a chess piece, not an abbreviation. – JɛﬀE Nov 3 '10 at 16:01

Your case is a lot easier, just choose $k$ of the $m$ columns and then you have $n (n-1)\ldots (n-k+1)$ ways to put the $k$ rooks. So the coefficient of $x^k$ is
$\displaystyle r_k = \binom{m}{k} n (n-1)\ldots (n-k+1) = \binom{m}{k}\binom{n}{k}k!$.
The provided link also gives a dynamic programming approach to compute $r_k$.