贪心算法之背包问题

 1 # coding=gbk
 2 # 完全背包问题，贪心算法
 3 import time
 4 __author__ = ‘ice‘
 5 
 6 
 7 class goods:
 8     def __init__(self, goods_id, weight=0, value=0):
 9         self.id = goods_id
10         self.weight = weight
11         self.value = value
12 
13 
14 # 不适用于0-1背包
15 def knapsack(capacity=0, goods_set=[]):
16     # 按单位价值量排序
17     goods_set.sort(key=lambda obj: obj.value / obj.weight, reverse=True)
18     result = []
19     for a_goods in goods_set:
20         if capacity < a_goods.weight:
21             break
22         result.append(a_goods)
23         capacity -= a_goods.weight
24     if len(result) < len(goods_set) and capacity != 0:
25         result.append(goods(a_goods.id, capacity, a_goods.value * capacity / a_goods.weight))
26     return result
27 
28 
29 some_goods = [goods(0, 2, 4), goods(1, 8, 6), goods(2, 5, 3), goods(3, 2, 8), goods(4, 1, 2)]
30 
31 start_time = time.clock()
32 res = knapsack(6, some_goods)
33 end_time = time.clock()
34 print(‘花费时间：‘ + str(end_time - start_time))
35 
36 for obj in res:
37     print(‘物品编号:‘ + str(obj.id) + ‘ ,放入重量:‘ + str(obj.weight) + ‘,放入的价值:‘ + str(obj.value), end=‘,‘)
38     print(‘单位价值量为:‘ + str(obj.value / obj.weight))
39 
40 
41 # 花费时间：2.2807240614677942e-05
42 # 物品编号:3 ,放入重量:2,放入的价值:8,单位价值量为:4.0
43 # 物品编号:0 ,放入重量:2,放入的价值:4,单位价值量为:2.0
44 # 物品编号:4 ,放入重量:1,放入的价值:2,单位价值量为:2.0
45 # 物品编号:1 ,放入重量:1,放入的价值:0.75,单位价值量为:0.75