Greedy priority-based search for suboptimal multi-agent path finding

Shao Hung Chan, Roni Stern, Ariel Felner, Sven Koenig

Research output: Contribution to journalConference articlepeer-review

4 Scopus citations


Multi-Agent Path Finding (MAPF) is the problem of finding collision-free paths, one for each agent, in a shared environment, while minimizing their sum of travel times. Since solving MAPF optimally is NP-hard, researchers have explored algorithms that solve MAPF suboptimally but efficiently. Priority-Based Search (PBS) is the leading algorithm for this purpose. It finds paths for individual agents, one at a time, and resolves collisions by assigning priorities to the colliding agents and replanning their paths during its search. However, PBS becomes ineffective for MAPF instances with high densities of agents and obstacles. Therefore, we introduce Greedy PBS (GPBS), which uses greedy strategies to speed up PBS by minimizing the number of collisions between agents. We then propose techniques that speed up GPBS further, namely partial expansions, target reasoning, induced constraints, and soft restarts. We show that GPBS with all these improvements has a higher success rate than the state-of-the-art suboptimal algorithm for a 1-minute runtime limit, especially for MAPF instances with small maps and dense obstacles.

Original languageEnglish
Pages (from-to)11-19
Number of pages9
JournalThe International Symposium on Combinatorial Search
Issue number1
StatePublished - 2023
Externally publishedYes
Event16th International Symposium on Combinatorial Search, SoCS 2023 - Prague, Czech Republic
Duration: 14 Jul 202316 Jul 2023

Bibliographical note

Publisher Copyright:
© 2023, Association for the Advancement of Artificial Intelligence (


The research at the University of Southern California was supported by the National Science Foundation (NSF) under grant numbers 1409987, 1724392, 1817189, 1837779, 1935712, 2121028, and 2112533, the United States-Israel Binational Science Foundation (BSF) under grant numbers 2019703 and 2021643, as well as a gift from Amazon Robotics. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the sponsoring organizations, agencies, or the U.S. government.

FundersFunder number
U.S. Government
National Science Foundation1409987, 1724392, 1935712, 2121028, 1837779, 1817189, 2112533
Bloom's Syndrome Foundation2019703, 2021643
United States-Israel Binational Science Foundation


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