Improved Outerplanarity Bounds for Planar Graphs
<|reference_start|>Improved Outerplanarity Bounds for Planar Graphs: In this paper, we study the outerplanarity of planar graphs, i.e., the number of times that we must (in a planar embedding that we can initially freely choose) remove the outerface vertices until the graph is empty. It is well-known that there are $n$-vertex graphs with outerplanarity $\tfrac{n}{6}+\Theta(1)$, and not difficult to show that the outerplanarity can never be bigger. We give here improved bounds of the form $\tfrac{n}{2g}+2g+O(1)$, where $g$ is the fence-girth, i.e., the length of the shortest cycle with vertices on both sides. This parameter $g$ is at least the connectivity of the graph, and often bigger; for example, our results imply that planar bipartite graphs have outerplanarity $\tfrac{n}{8}+O(1)$. We also show that the outerplanarity of a planar graph $G$ is at most $\tfrac{1}{2}$diam$(G)+O(\sqrt{n})$, where diam$(G)$ is the diameter of the graph. All our bounds are tight up to smaller-order terms, and a planar embedding that achieves the outerplanarity bound can be found in linear time.<|reference_end|>
@article{biedl2024improved,
    title={Improved Outerplanarity Bounds for Planar Graphs},
    author={Therese Biedl and Debajyoti Mondal},
    journal={arXiv preprint arXiv:2407.04282},
    year={2024},
    archivePrefix={arXiv},
    eprint={2407.04282},
    primaryClass={cs.DS cs.DM}
}