Lempel–Ziv-78 Compressed String Dictionaries

String dictionaries store a collection ( s_i) _0≤ i < m of m variable-length keys (strings) over an alphabet and support the operations lookup (given a string s∈ ^* , decide if s_i=s for some i , and return this i ) and access (given an integer 0≤ i < m , return the string s_i ). We show how to modify the Lempel–Ziv-78 data compression algorithm to store the strings space-efficiently and support the operations lookup and access in optimal time. Our approach is validated experimentally on dictionaries of up to 1.5 GB of uncompressed text. We achieve compression ratios often outperforming the existing alternatives, especially on dictionaries containing many repeated substrings. Our query times remain competitive.