You have to start and end at certain points

This type of problem, classified as NP-complete,is notoriously difficult when the graph is sufficiently large.Although any proposed solution can be easily verified,we have no reliable formula or shortcut for finding one,or determining that one exists.And we're not even sure if it's possible for computers to reliably find such solutions, either.This puzzle adds a twist to the Hamiltonian path problem in that you have to start and end at specific points.