说明：  旅行商问题 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。 例如：给定4个城市{1，2，3，4}及其各城市之间的路程 最优路线是1,3,2,4,1， 其最短路程是25
(a salesman, traveling salesman problem, a number of cities to sell commodities, the known distance between the city (or travel). He selected from a resident, after each city again, the last resident to return to the line, making the total distance (or travel) is the smallest. For example : given four cities (1,2,3,4) and the distance between the city optimal route is 1,3,2,4, 1, the shortest distance is 25)