Planar Graphs as VPG-Graphs
Vol. 17, no. 4, pp. 475-494, 2013. Regular paper.
Abstract A graph is Bk-VPG when it has an intersection representation by paths in a rectangular grid with at most k bends (turns). It is known that all planar graphs are B3-VPG and this was conjectured to be tight. We disprove this conjecture by showing that all planar graphs are B2-VPG. We also show that the 4-connected planar graphs constitute a subclass of the intersection graphs of Z-shapes (i.e., a special case of B2-VPG). Additionally, we demonstrate that a B2-VPG representation of a planar graph can be constructed in O(n3/2) time. We further show that the triangle-free planar graphs are contact graphs of: L-shapes, Γ-shapes, vertical segments, and horizontal segments (i.e., a special case of contact B1-VPG). From this proof we obtain a new proof that bipartite planar graphs are a subclass of 2-DIR.
Submitted: December 2012.
Reviewed: March 2013.
Revised: April 2013.
Accepted: May 2013.
Final: July 2013.
Published: July 2013.
Communicated by Walter Didimo and Maurizio Patrignani
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