ClearConcept — A-Level Revision

Specification Reference

Dictionary encoding

Standard

Plain English

Lossless compression replacing frequent patterns with shorter codes using a dictionary. Huffman and LZ77 variants exemplify dictionary-based encoding. Adaptive dictionaries build during encoding.

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Real World

When you create a .zip file on your laptop, the ZIP algorithm uses LZ77 dictionary encoding to spot repeated byte patterns across the file and replace them with short back-references.

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Exam Focus

Distinguish dictionary encoding from RLE clearly — dictionary replaces repeated patterns; RLE replaces consecutive identical values.

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