Hamiltonian cycles and paths in hypercubes with disjoint faulty edges

Abstract

We consider hypercubes with pairwise disjoint faulty edges. An $n$-dimensional hypercube $Q_n$ is an undirected graph with $2^n$ nodes, each labeled with a distinct binary strings of length $n$. The parity of the vertex is 0 if the number of ones in its labels is even, and is 1 if the number of ones is odd. Two vertices $a$ and $b$ are connected by the edge iff $a$ and $b$ differ in one position. If $a$ and $b$ differ in position $i$, then we say that the edge $(a,b)$ goes in direction $i$ and we define the parity of the edge as the parity of the end with 0 on the position $i$. It was already known that $Q_n$ is not Hamiltonian if all edges going in one direction and of the same parity are faulty. In this paper we show that if $n\ge4$ then all other hypercubes are Hamiltonian. In other words, every cube $Q_n$, with $n\ge4$ and disjoint faulty edges is Hamiltonian if and only if for each direction there are two healthy crossing edges of different parity.