Which of the following is not a variable length encoding?

LZW encoding uses fixed-length codes , not variable-length. The others (Huffman, Shannon-Fano, Adaptive Huffman) are variable-length encodings . Important Points (English) LZW (Lempel–Ziv–Welch) encoding uses fixed-length codes during encoding.

LZW works by building a dictionary dynamically and replacing repeated strings with fixed-size codewords.

Since code length remains constant, LZW decoding is simpler and faster .

Huffman encoding uses variable-length codes , where frequent symbols get shorter codes.

Shannon–Fano encoding is also variable-length , based on symbol probabilities.

Adaptive Huffman encoding updates code lengths dynamically, so it is variable-length as well.

Variable-length encodings generally achieve better compression than fixed-length methods.