Periods, Partial Words, and a Result of Guibas and Odlyzko |
F. Blanchet-Sadri and Brian Shirey |
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A well known and unexpected result of Guibas and
Odlyzko states that the set of all periods of a word is independent of the
alphabet size (alphabets with one symbol are excluded here).
More specifically, for every word u,
there exists a word v over the
alphabet {0,1} such that u and
v have the same length and the same set of periods. Recently,
Blanchet-Sadri and Chriscoe extended this fundamental result to words with one
"do not know" symbol also called partial words with one hole.
They showed that for every partial word u with one hole,
there exists a partial word v with at most one hole over the alphabet {0,1}
such that u and v
have the same length, the same set of periods, the same set of weak
periods, and H(v) Ì H(u), where H(u)
(respectively, H(v)) denotes the set of holes of u
(respectively, v). In this paper, we extend
this result further to a large class of partial words.
Given a partial word u belonging to that class,
our proof provides an algorithm to compute a partial word v
over {0,1} sharing the same length and same sets of periods and weak periods as u,
and satisfying H(v) Ì H(u).
Keywords: Words, partial words, periods, and weak periods. |
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