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Published in:
2007 | OriginalPaper | Chapter
On Demand String Sorting over Unbounded Alphabets
Authors : Carmel Kent, Moshe Lewenstein, Dafna Sheinwald
Published in: Combinatorial Pattern Matching
Publisher: Springer Berlin Heidelberg
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On-demand string sorting is the problem of preprocessing a set of
n
strings to allow subsequent queries of finding the
k
<
n
lexicographically smallest strings (and afterwards the next
k
etc.) This on-demand variant strongly resembles the search engine queries which give you the best
k
-ranked pages recurringly.
We present a data structure that supports this in
O
(
n
) preprocessing time, and answers queries in
O
(log
n
) time. There is also a cost of
O
(
N
) time amortized over all operations, where
N
is the total length of the strings.
Our data structure is a heap of strings, which supports heapify and delete-mins. As it turns out, implementing a full heap with all operations is not that simple. For the sake of completeness we propose a heap with full operations based on balanced indexing trees that supports the heap operations in optimal times.