某售货员要到若干城市去推销商品，已知个城市之间的路程或路费，我要选定一条从驻地出发，经过每个城市一次，最后回到驻地的路线，使总的路程（或路费）最小。（回溯法）(A salesperson will sell products to several cities. The distance or distance between the known cities will be chosen. I will choose a route that starts from the station,