Question

我几乎完成了计算我的背包问题。我有一个项目列表，其权重（磅）和价值。我的背包不能超过11磅。

我无法弄清楚计算和打印出以下内容的最后一段代码： 1.要带的最佳项目清单 2.总重量 3.项目总价值

请参阅下面的我目前的代码：

# Potential items to bring in knapsack 

items = (
    ("t-shirt", 0.53, 15), 
    ("trousers", 1.06, 10), 
    ("waterproof trousers", 0.93, 70), 
    ("waterproof overclothes", 0.95, 75),
    ("socks", 0.09, 50), 
    ("backpack & gear packaging", 1.9, 300), 
    ("sleeping gear & tent/shelter", 2.8, 260), 
    ("hammock", 2.8, 120),
    ("cooking gear & water storage", 0.8, 240),
    ("map", 0.2, 150), 
    ("compass", 0.29, 35), 
    ("glucose", 0.33, 60), 
    ("tin", 1.5, 45),
    ("sunscreen", 0.24, 70), 
    ("first aid kit", 1.3, 90), 
    ("umbrella", 1.61, 40), 
    ("water (1 pint)", 1, 200),
    ("food (3 days)", 4.5, 190), 
    ("fuel", 0.2, 190), 
    ("camera", 0.71, 30),
    ("beer", 1.15, 10), 
    ("towel", 0.4, 12),
    ("book", 0.66, 10),
    ("sunglasses", 0.15, 20),
    ("notebook", 0.49, 80)
)

from itertools import combinations

def combinations_func(items):
    """ return any combination from list of potential items for knapsack """ 
    return (combination
            for r in range(1, len(items)+1)
            for combination in combinations(items, r))

def totalvalue_func(combination):
    """ calculate total value for a combination of knapsack items """
    total_weight = 0
    total_value = 0
    for item, weight, value in combination:
        total_weight += weight
        total_value += value 
    return (total_value, -total_weight) if total_weight <= 11 else (0,0)

任何帮助将不胜感激！

Answer 1

按照您的想法，您需要迭代所有组合并选择最佳解决方案。顺便说一句，这个算法的时间复杂度是O（2 ^ N），非常低效。

max_value = -float('Inf')
weight = None
optimal_items = None
for comb in combinations_func(items):
    total_value, total_weight = totalvalue_func(comb)
    if total_value > max_value:
        max_value = total_value
        weight = total_weight
        optimal_items = comb

print(max_value)
print(weight)
print(optimal_items)

输出：

1820
10.74
(('waterproof overclothes', 0.95, 75), ('socks', 0.09, 50), ('backpack & gear packaging', 1.9, 300), ('sleeping gear & tent/shelter', 2.8, 260), ('cooking gear & water storage', 0.8, 240), ('map', 0.2, 150), ('compass', 0.29, 35), ('glucose', 0.33, 60), ('sunscreen', 0.24, 70), ('first aid kit', 1.3, 90), ('water (1 pint)', 1, 200), ('fuel', 0.2, 190), ('sunglasses', 0.15, 20), ('notebook', 0.49, 80))

Python：坚持最后一块背包计算

1 个答案: