Editing Hamiltonian path problem (section)

=== Unconventional methods ===
Because of the difficulty of solving the Hamiltonian path and cycle problems on conventional computers, they have also been studied in unconventional models of computing. For instance, [[Leonard Adleman]] showed that the Hamiltonian path problem may be solved using a [[DNA computing|DNA computer]]. Exploiting the parallelism inherent in chemical reactions, the problem may be solved using a number of chemical reaction steps linear in the number of vertices of the graph; however, it requires a factorial number of DNA molecules to participate in the reaction.<ref>{{citation |last=Adleman |first=Leonard |title=Molecular computation of solutions to combinatorial problems |date=November 1994 |journal=[[Science (journal)|Science]] |volume=266 |issue=5187 |pages=1021–1024 |bibcode=1994Sci...266.1021A |citeseerx=10.1.1.54.2565 |doi=10.1126/science.7973651 |jstor=2885489 |pmid=7973651 |author-link=Leonard Adleman}}.</ref>

An optical solution to the Hamiltonian problem has been proposed as well.<ref name="oltean_hamiltonian2">{{cite conference |author=Mihai Oltean |date=2006 |title=A light-based device for solving the Hamiltonian path problem |conference=Unconventional Computing |publisher=Springer LNCS 4135 |pages=217–227 |arxiv=0708.1496 |doi=10.1007/11839132_18}}</ref> The idea is to create a graph-like structure made from optical cables and beam splitters which are traversed by light in order to construct a solution for the problem. The weak point of this approach is the required amount of energy which is exponential in the number of nodes.