NP-complete problems are a class of problems in computer science for which no efficient [[algorithm]] exists. Interestingly, if an efficient algorithm works for any one instance of an NP-complete problem, an efficient algorithm can be found for all of them. If you'd like to win a Nobel Prize or make a lot of money, consider trying to find an efficient solution for an NP-complete problem. However, its probably best to show that the problem is NP-complete and instead find an efficient approximation algorithm. The [[traveling salesperson problem]] is a classic example of an NP-complete problem. (The version of the traveling salesperson problem that is NP-complete asks whether there exists an order of stops whose distance totals at most a given amount.)