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arXiv · 2301.07757

Freeze-Tag is NP-Hard in 3D with $L_1$ distance

Lucas de Oliveira Silva
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Abstract

Arkin et al. in 2002 introduced a scheduling-like problem called Freeze-Tag Problem (FTP) motivated by robot swarm activation. The input consists of the locations of n mobile punctual robots in some metric space or graph. Only one begins "active", while the others are initially "frozen". All active robots can move at unit speed and, upon reaching a frozen one's location, activates it. The goal is to activate all the robots in the minimum amount of time, the so-called makespan. Until 2017 the hardness of this problem in metric spaces was still open, but then Yu et al. proved it to be NP-Hard in the Euclidian plane, and in the same year, Demaine and Roudoy demonstrated that the FTP is also hard in 3D with any $L_p$ distance (with p > 1). However, we still don't know whether Demaine's and Roudoy's result could be translated to the plane. This paper fills the p=1 gap by showing that the FTP is NP-Hard in 3D with $L_1$ distance.

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Lucas de Oliveira Silva. 2023-01-18. Freeze-Tag is NP-Hard in 3D with $L_1$ distance. https://arxiv.org/abs/2301.07757

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