backtrackng

代码说明：

  给定n种物品和一背包。物品i的重量是wi>0,价值为vi>0,背包的容量为c。选择装入背包的物品，使得装入背包中物品的总价值最大。(Given n kinds of goods and a backpack. Weight of the item i is wi> 0, the value of vi> 0, knapsack capacity c. Select the items into the backpack, so into the backpack of items in the total value of the maximum.)