Given a sequence S of n symbols over some alphabet Σ of size
σ, we develop new compression methods that are (i) very simple
to implement; (ii) provide O(1) time random access to any symbol (or short
substring) of the original sequence. Our simplest solution uses at most 2h+o(h)
bits of space, where h = n(H
$_{0}$
(S)+1), and
H
$_{0}$
(S) is the zeroth-order empirical
entropy of S. We discuss a number of improvements and trade-offs over the basic
method. For example, we can achieve n(H
$_{k}$
(S)+1)+o(n(H
$_{k}$
(S)+1))
bits of space, for
k = o(log
$_{σ}$
(n)). Several applications are discussed, including text compression,
(compressed) full-text indexing and string matching.
