The Traveling Salesman Problem
•Question: Given n vertices, how many different cycles Cn can we form by connecting these vertices with edges?
•Solution: We first choose a starting point. Then we have (n – 1) choices for the second vertex in the cycle, (n – 2) for the third one, and so on, so there are (n – 1)! choices for the whole cycle.
•However, this number includes identical cycles that were constructed in opposite directions. Therefore, the actual number of different cycles Cn is (n – 1)!/2.