60 lines
1.7 KiB
Python
60 lines
1.7 KiB
Python
#!/usr/bin/python
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# -*- coding: UTF-8 -*-
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from typing import List
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# 背包选取的物品列表
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picks = []
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picks_with_max_value = []
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def bag(capacity: int, cur_weight: int, items_info: List, pick_idx: int):
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"""
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回溯法解01背包，穷举
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:param capacity: 背包容量
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:param cur_weight: 背包当前重量
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:param items_info: 物品的重量和价值信息
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:param pick_idx: 当前物品的索引
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:return:
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"""
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# 考察完所有物品，或者在中途已经装满
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if pick_idx >= len(items_info) or cur_weight == capacity:
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global picks_with_max_value
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if get_value(items_info, picks) > \
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get_value(items_info, picks_with_max_value):
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picks_with_max_value = picks.copy()
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else:
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item_weight = items_info[pick_idx][0]
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if cur_weight + item_weight <= capacity: # 选
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picks[pick_idx] = 1
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bag(capacity, cur_weight + item_weight, items_info, pick_idx + 1)
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picks[pick_idx] = 0 # 不选
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bag(capacity, cur_weight, items_info, pick_idx + 1)
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def get_value(items_info: List, pick_items: List):
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values = [_[1] for _ in items_info]
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return sum([a*b for a, b in zip(values, pick_items)])
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if __name__ == '__main__':
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# [(weight, value), ...]
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items_info = [(3, 5), (2, 2), (1, 4), (1, 2), (4, 10)]
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capacity = 8
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print('--- items info ---')
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print(items_info)
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print('\n--- capacity ---')
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print(capacity)
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picks = [0] * len(items_info)
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bag(capacity, 0, items_info, 0)
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print('\n--- picks ---')
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print(picks_with_max_value)
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print('\n--- value ---')
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print(get_value(items_info, picks_with_max_value))
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