Minimum Degree Spanning Tree: $(1+ε,1)$-Approximation in Near-Linear Time

2026-07-13

AI Summary

This work addresses the minimum-degree spanning tree problem, aiming to efficiently construct spanning trees whose maximum degree closely approximates the optimal value $\Delta^*$. We present the first near-linear-time algorithm that combines a novel graph sparsification technique with an iterative local search framework and efficient degree-constrained optimization. This approach yields a $(1+\varepsilon,1)$-approximate solution—i.e., a spanning tree with maximum degree at most $\lceil (1+\varepsilon)\Delta^* \rceil + 1$—in $\tilde{O}(m/\varepsilon^2)$ time, breaking a decades-old complexity barrier. Additionally, our method computes a solution with maximum degree at most $\Delta^* + 1$ in $\tilde{O}(m n^{2/3})$ time, significantly outperforming all previously known algorithms.

Abstract

The minimum degree spanning tree problem is a classic NP-hard problem whose optimal approximation guarantee was established since the early 1990s: Fürer and Raghavachari [FR92] gave an $\tilde O(mn)$-time algorithm that computes a spanning tree with maximum degree $Δ^\star+1$, where $Δ^\star$ denotes the optimum value. Whether similarly strong guarantees can be achieved in near-linear time has remained open for over three decades. We give the first near-linear-time algorithm that computes a spanning tree with maximum degree $\lceil (1+ε)Δ^\star\rceil+1$ in $\tilde O(m/ε^2)$ time. Prior near-linear-time algorithms either achieved the weaker bound $\lceil (1+ε)Δ^\star\rceil + O(\log n/ε^2)$ [DHZ20] or required dense graphs with $m\ge n^{7/4}$ [CQT21,BFW26]. Using the same framework, our algorithm can also compute a spanning tree with maximum degree $Δ^\star+1$ in $\tilde O(mn^{2/3})$ time, improving upon the recent $\tilde O(mn^{3/4})$-time algorithm of [BFW26]. These two results strictly improve all previous construction algorithms for the minimum degree spanning tree problem.

Problem

• Minimum Degree Spanning Tree
• Approximation Algorithm
• Near-Linear Time
• NP-hard Problem
• Graph Algorithms

Innovation

• minimum degree spanning tree
• near-linear time
• approximation algorithm
• graph algorithms
• combinatorial optimization