_移位实现 某售货员要到若干城市去推销商品，已知各城市之间的路程（或旅费）。他要选定一条从驻地出发，经过每个城市一遍，最后回到驻地的路线，使总的路程（或旅费）最小。-_ Shift to achieve a salesman to a number of cities to sell commodities, known distance between cities (or travel). He has to select a departure from the resident,