Canonical Coin Systems for Change-Making Problems

TL;DR

This paper investigates the conditions under which the greedy algorithm guarantees optimal solutions for the change-making problem, providing new proofs and an efficient decision algorithm for canonical coin systems.

Contribution

It offers new proofs for canonical coin system conditions and introduces an $O(m^2)$ algorithm to determine if a coin system is canonical.

Findings

Greedy algorithm is optimal for certain coin systems.

New proofs for canonical coin system conditions.

Efficient $O(m^2)$ algorithm to decide canonicity.

Abstract

The Change-Making Problem is to represent a given value with the fewest coins under a given coin system. As a variation of the knapsack problem, it is known to be NP-hard. Nevertheless, in most real money systems, the greedy algorithm yields optimal solutions. In this paper, we study what type of coin systems that guarantee the optimality of the greedy algorithm. We provide new proofs for a sufficient and necessary condition for the so-called \emph{canonical} coin systems with four or five types of coins, and a sufficient condition for non-canonical coin systems, respectively. Moreover, we present an $O(m^2)$ algorithm that decides whether a tight coin system is canonical.