给定n种物品和一重量为M背包。物品i的重量是wi。问应如何选择装入背包的物品，使得装入背包中物品的总重量恰好为M，找出问题的所有解。-Given n types of items and a weight of M backpack. Item i is the weight wi. Asked how to choose the items into the bag, making the items into a backpack just for the total weight of M, find all solutions of the problem.