已知n个城市之间的相互距离，现有一个推销员必须遍访这n个城市，并且每个城市只能访问一次，最后又必须返回出发城市。如何安排他对这些城市的访问次序，可使其旅行路线的总长度最短？ -Known n city between the distance, the existing of a salesman to be visited this n city, and each city can only be visited once, finally to return to the starti