A Generic Top-Down Dynamic-Programming Approach to Prefix-Free Coding

TL;DR

This paper demonstrates that a top-down dynamic programming approach to prefix-free coding problems can be significantly accelerated using batching techniques, leading to faster solutions for various coding variations.

Contribution

It introduces a structural property enabling batching in DP calculations, resulting in an order of magnitude speedup for multiple prefix-free coding algorithms.

Findings

Speedup of an order of magnitude for coding algorithms

Applicability to mixed radix, reserved length, and one-ended coding

Structural property enabling batching in dynamic programming

Abstract

Given a probability distribution over a set of n words to be transmitted, the Huffman Coding problem is to find a minimal-cost prefix free code for transmitting those words. The basic Huffman coding problem can be solved in O(n log n) time but variations are more difficult. One of the standard techniques for solving these variations utilizes a top-down dynamic programming approach. In this paper we show that this approach is amenable to dynamic programming speedup techniques, permitting a speedup of an order of magnitude for many algorithms in the literature for such variations as mixed radix, reserved length and one-ended coding. These speedups are immediate implications of a general structural property that permits batching together the calculation of many DP entries.