sequences and series - Find all polynomials $sum_{k=0}^na_kx^k$, where $a_k=pm2$ or $a_k=pm1$, and $0leq kleq n,1leq n

Find all polynomials $\sum_{k=0}^na_kx^k$, where $a_k=\pm2$ or $a_k=\pm1$, and $0\leq k\leq n,1\leq n<\infty$, such that they have only real zeroes.

I've been thinking about this question, but I've come to the conclusion that I don't have the requisite math knowledge to actually answer it.

An additional, less-important question. I'm not sure where this problem is from. Can someone find a source?

edit

I'm sorry, I have one more request. If this can be evaluated computationally, can you show me a pen and paper way to do it?