Complete characterization of disconnected one-point unions of cycles with local antimagic chromatic number 2

Abstract: A graph $G = (V, E)$ that admits a bijective edge labeling $f:E \to{1,\ldots ,|E|}$ is local antimagic if $f$ induces a vertex labeling $f<sup>+$ such that for any pair of adjacent vertices $x$ and $y$, $f^+(x)\not= f<sup>+(y)$, where the induced vertex label $f^+(x)= \sum f(xu)$, with $u$ ranging over all the vertices adjacent to $x$. The minimum number of distinct induced vertex labels over all local antimagic labelings of $G$ is the local antimagic chromatic number of $G$, denoted $χ_{la}(G)$. In this paper, we completely characterize all the disconnected one-point unions of cycles (having at most 3 components) with local antimagic chromatic number 2. Our approach allows the complete characterization of all such graphs with at least 4 components by a case-by-case analysis and every edge is assigned a unique label, up to isomorphism.