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cs.DM2010
Multi-Shift de Bruijn Sequence
Zhi Xu
A (non-circular) de Bruijn sequence w of order n is a word such that every word of length n appears exactly once in w as a factor. In this paper, we generalize the concept to a mul…
cs.DM2008★ 4 cited
An NP-hardness Result on the Monoid Frobenius Problem
Zhi Xu, J. Shallit
The following problem is NP-hard: given a regular expression , decide if is not co-finite.
cs.DM2007
The Frobenius Problem in a Free Monoid
Jui-Yi Kao, Jeffrey Shallit, Zhi Xu
The classical Frobenius problem is to compute the largest number g not representable as a non-negative integer linear combination of non-negative integers x_1, x_2, ..., x_k, where…