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52 lines
1.2 KiB
52 lines
1.2 KiB
=begin
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File: fractional_knapsack.rb
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Created Time: 2024-05-07
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Author: Xuan Khoa Tu Nguyen (ngxktuzkai2000@gmail.com)
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=end
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### 物品 ###
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class Item
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attr_accessor :w # 物品重量
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attr_accessor :v # 物品價值
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def initialize(w, v)
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@w = w
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@v = v
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end
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end
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### 分數背包：貪婪 ###
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def fractional_knapsack(wgt, val, cap)
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# 建立物品串列，包含兩個屬性：重量，價值
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items = wgt.each_with_index.map { |w, i| Item.new(w, val[i]) }
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# 按照單位價值 item.v / item.w 從高到低進行排序
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items.sort! { |a, b| (b.v.to_f / b.w) <=> (a.v.to_f / a.w) }
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# 迴圈貪婪選擇
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res = 0
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for item in items
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if item.w <= cap
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# 若剩餘容量充足，則將當前物品整個裝進背包
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res += item.v
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cap -= item.w
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else
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# 若剩餘容量不足，則將當前物品的一部分裝進背包
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res += (item.v.to_f / item.w) * cap
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# 已無剩餘容量，因此跳出迴圈
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break
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end
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end
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res
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end
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### Driver Code ###
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if __FILE__ == $0
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wgt = [10, 20, 30, 40, 50]
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val = [50, 120, 150, 210, 240]
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cap = 50
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n = wgt.length
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# 貪婪演算法
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res = fractional_knapsack(wgt, val, cap)
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puts "不超過背包容量的最大物品價值為 #{res}"
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end
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