1 research outputs found
Twenty (or so) Questions: -ary Length-Bounded Prefix Coding
Efficient optimal prefix coding has long been accomplished via the Huffman
algorithm. However, there is still room for improvement and exploration
regarding variants of the Huffman problem. Length-limited Huffman coding,
useful for many practical applications, is one such variant, for which codes
are restricted to the set of codes in which none of the codewords is longer
than a given length, . Binary length-limited coding can be done in
time and O(n) space via the widely used Package-Merge algorithm
and with even smaller asymptotic complexity using a lesser-known algorithm. In
this paper these algorithms are generalized without increasing complexity in
order to introduce a minimum codeword length constraint , to allow
for objective functions other than the minimization of expected codeword
length, and to be applicable to both binary and nonbinary codes; nonbinary
codes were previously addressed using a slower dynamic programming approach.
These extensions have various applications -- including fast decompression and
a modified version of the game ``Twenty Questions'' -- and can be used to solve
the problem of finding an optimal code with limited fringe, that is, finding
the best code among codes with a maximum difference between the longest and
shortest codewords. The previously proposed method for solving this problem was
nonpolynomial time, whereas solving this using the novel linear-space algorithm
requires only time, or even less if is not .Comment: 12 pages, 4 figures, extended version of cs/0701012 (accepted to ISIT
2007), formerly "Twenty (or so) Questions: -ary Bounded-Length Huffman
Coding