A Deterministic Polynomial-time Approximation Scheme for Counting Knapsack Solutions

Given n elements with nonnegative integer weights w1,..., wn and an integer capacity C, we consider the counting version of the classic knapsack problem: find the number of distinct subsets whose weights add up to at most the given capacity. We give a deterministic algorithm that estimates the number of solutions to within relative error 1+-eps in time polynomial in n and 1/eps (fully polynomial approximation scheme). More precisely, our algorithm takes time O(n^3 (1/eps) log (n/eps)). Our algorithm is based on dynamic programming. Previously, randomized polynomial time approximation schemes were known first by Morris and Sinclair via Markov chain Monte Carlo techniques, and subsequently by Dyer via dynamic programming and rejection sampling.