Algorithm Engineering of SSSP With Negative Edge Weights

TL;DR

This paper explores the practical implementation of a recent near-linear time algorithm for shortest path problems with negative weights, demonstrating significant speed improvements over traditional methods on difficult instances.

Contribution

It provides the first extensive practical implementation and evaluation of the recent combinatorial algorithm for SSSP with negative weights, including parameter tuning and comparison with existing algorithms.

Findings

Implementation achieves up to 100x speedup on hard instances.

Parameter tuning significantly impacts performance.

The algorithm is practical and competitive with state-of-the-art methods.

Abstract

Computing shortest paths is one of the most fundamental algorithmic graph problems. It is known since decades that this problem can be solved in near-linear time if all weights are nonnegative. A recent break-through by [Bernstein, Nanongkai, Wulff-Nilsen '22] presented a randomized near-linear time algorithm for this problem. A subsequent improvement in [Bringmann, Cassis, Fischer '23] significantly reduced the number of logarithmic factors and thereby also simplified the algorithm. It is surprising and exciting that both of these algorithms are combinatorial and do not contain any fundamental obstacles for being practical. We launch the, to the best of our knowledge, first extensive investigation towards a practical implementation of [Bringmann, Cassis, Fischer '23]. To this end, we give an accessible overview of the algorithm, discussing what adaptions are necessary to obtain a fast algorithm in practice. We manifest these adaptions in an efficient implementation. We test our implementation on a benchmark data set that is adapted to be more difficult for our implementation in order to allow for a fair comparison. As in [Bringmann, Cassis, Fischer '23] as well as in our implementation there are multiple parameters to tune, we empirically evaluate their effect and thereby determine the best choices. Our implementation is then extensively compared to one of the state-of-the-art algorithms for this problem [Goldberg, Radzik '93]. On the hardest instance type, we are faster by up to almost two orders of magnitude.