Spanning directed trees with many leaves

Noga Alon, Fedor V. Fomin, Gregory Gutin*, Michael Krivelevich, Saket Saurabh

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


The DIRECTED MAXIMUM LEAF OUT-BRANCHING problem is to find an out-branching (i.e., a rooted oriented spanning tree) in a given digraph with the maximum number of leaves. In this paper, we obtain two combinatorial results on the number of leaves in out-branchings. We show that (1) every strongly connected n-vertex digraph D with minimum in-degree at least 3 has an outbranching with at least (n/4)1/3 - 1 leaves; (2) if a strongly connected digraph D does not contain an out-branching with k leaves, then the pathwidth of its underlying graph UG(D) is O(k log k), and if the digraph is acyclic with a single vertex of in-degree zero, then the pathwidth is at most 4k. The last result implies that it can be decided in time 2O(k log2 k) · nO(1) whether a strongly connected digraph on n vertices has an out-branching with at least k leaves. On acyclic digraphs the running time of our algorithm is 2O(k log k) · nO(1).

Original languageEnglish
Pages (from-to)466-476
Number of pages11
JournalSIAM Journal on Discrete Mathematics
Issue number1
StatePublished - 2008


FundersFunder number
Engineering and Physical Sciences Research CouncilEP/E034985/1


    • Directed graphs
    • Fixed parameter tractability
    • Maximum leaf
    • Out-branching
    • Rooted tree


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