On Hamiltonicity of image-free graphs

An st-path is a path with the end-vertices s and t. An s-path is a path with an end-vertex s. The results of this paper include necessary and sufficient conditions for a image-free graph G with image and image to have (1) a Hamiltonian s-path, (2) a Hamiltonian st-path, (3) a Hamiltonian s- and st-paths containing e when G has connectivity one, and (4) a Hamiltonian cycle containing e when G is 2-connected. These results imply that a connected image-free graph has a Hamiltonian path and a 2-connected image-free graph has a Hamiltonian cycle [D. Duffus, R.J. Gould, M.S. Jacobson, Forbidden subgraphs and the Hamiltonian theme, in: The Theory and Application of Graphs (Kalamazoo, Mich., 1980), Wiley, New York, 1981, pp. 297–316]. Our proofs of (1)–(4) are shorter than the proofs of their corollaries in [D. Duffus, R.J. Gould, M.S. Jacobson, Forbidden subgraphs and the Hamiltonian theme, in: The Theory and Application of Graphs (Kalamazoo, Mich., 1980), Wiley, New York, 1981, pp. 297–316], and provide polynomial-time algorithms for solving the corresponding Hamiltonicity problems.