背包问题：设有不同价值、不同重量的物件n件，求从n件物品中选取一部分物品的方案，使选中物品的总重量不超过指定的限制重量，但选中物品的总价值最大。-Knapsack problem: has different values, different weights of objects n pieces, find some items selected　n items in the program, bringing the total weight of the selected items does not exceed the specified weight limit, but the maximum total value of selected items.