More on spanning 2-connected subgraphs of alphabet graphs, special classes of grid graphs
Muhammad Salman, Hajo Broersma, C. A. Rodger · University of Twente Research Information · 2002
A grid graph $G$ is a finite induced subgraph of the infinite 2-dimensional grid defined by $Z \\times Z$ and all edges between pairs of vertices from $Z \\times Z$ at Euclidean distance precisely 1. A natural drawing of $G$ is obtained by drawing its vertices in $\\mathbb{R}^2$ according to their coordinates. Apart from the outer face, all (inner) faces with area exceeding one (not bounded by a 4-cycle) in a natural drawing of $G$ are called the holes of $G$. We define 26 classes of grid graphs called alphabet graphs, with no or a few holes. We determine which of the alphabet graphs contain a Hamilton cycle, i.e. a cycle containing all vertices, and solve the problem of determining a spanning 2-connected subgraph with as few edges as possible for all alphabet graphs.