LZ78s

LZ78s is a lossless data compression algorithm developed by Abraham Lempel and Jacob Ziv in 1978. It is a dictionary-based compression method, meaning it builds a dictionary of frequently occurring patterns within the data and replaces those patterns with references to the dictionary. Unlike its predecessor LZ77, which used a sliding window, LZ78s explicitly constructs a dictionary table.

The algorithm works by reading the input data and, for each new character encountered, searching for the longest prefix of the current data that already exists in the dictionary. If such a prefix is found, the algorithm concatenates the current character to this prefix and checks if the resulting string is in the dictionary. If it is, it continues extending the prefix. If it is not, the algorithm outputs the code for the existing prefix and the new character, and then adds the new string (prefix + character) to the dictionary. The dictionary is typically initialized with all single characters.

LZ78s is known for its simplicity and effectiveness on a wide range of data. Its performance depends on the redundancy of the input data. The size of the dictionary can grow considerably, which is a factor in its memory usage. Variations and improvements on the LZ78 algorithm exist, such as LZW (Lempel-Ziv-Welch), which is widely used in various applications.