有n个城市，一个推销员要从其中的某一个城市出发，每个城市只能遍历一次，要求走遍所有的城市，再回到他出发的城市，求所有可能路径中路径最短的一条路径来-N cities, a salesman from which a city departure, each city can only traverse requirements went through all of the city, and then returned to the city of his departure, seeking