TY - JOUR

T1 - Out-degree reducing partitions of digraphs

AU - Bang-Jensen, Jørgen

AU - Yeo, Anders

AU - Bessy, Stephane

AU - Havet, Frederic

PY - 2018

Y1 - 2018

N2 - Let k be a fixed integer. We determine the complexity of finding a p-partition (V1,…,Vp) of the vertex set of a given digraph such that the maximum out-degree of each of the digraphs induced by Vi, (1≤i≤p) is at least k smaller than the maximum out-degree of D. We show that this problem is polynomial-time solvable when p≥2k and NP-complete otherwise. The result for k=1 and p=2 answers a question posed in [3]. We also determine, for all fixed non-negative integers k1,k2,p, the complexity of deciding whether a given digraph of maximum out-degree p has a 2-partition (V1,V2) such that the digraph induced by Vi has maximum out-degree at most ki for i∈[2]. It follows from this characterization that the problem of deciding whether a digraph has a 2-partition (V1,V2) such that each vertex v∈Vi has at least as many neighbours in the set V3−i as in Vi, for i=1,2 is NP-complete. This solves a problem from [6] on majority colourings.

AB - Let k be a fixed integer. We determine the complexity of finding a p-partition (V1,…,Vp) of the vertex set of a given digraph such that the maximum out-degree of each of the digraphs induced by Vi, (1≤i≤p) is at least k smaller than the maximum out-degree of D. We show that this problem is polynomial-time solvable when p≥2k and NP-complete otherwise. The result for k=1 and p=2 answers a question posed in [3]. We also determine, for all fixed non-negative integers k1,k2,p, the complexity of deciding whether a given digraph of maximum out-degree p has a 2-partition (V1,V2) such that the digraph induced by Vi has maximum out-degree at most ki for i∈[2]. It follows from this characterization that the problem of deciding whether a digraph has a 2-partition (V1,V2) such that each vertex v∈Vi has at least as many neighbours in the set V3−i as in Vi, for i=1,2 is NP-complete. This solves a problem from [6] on majority colourings.

U2 - 10.1016/j.tcs.2017.11.007

DO - 10.1016/j.tcs.2017.11.007

M3 - Journal article

SN - 0304-3975

VL - 719

SP - 64

EP - 72

JO - Theoretical Computer Science

JF - Theoretical Computer Science

ER -