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51 lines
1.4 KiB
51 lines
1.4 KiB
=begin
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File: coin_change_greedy.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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### 零錢兌換：貪婪 ###
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def coin_change_greedy(coins, amt)
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# 假設 coins 串列有序
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i = coins.length - 1
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count = 0
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# 迴圈進行貪婪選擇，直到無剩餘金額
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while amt > 0
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# 找到小於且最接近剩餘金額的硬幣
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while i > 0 && coins[i] > amt
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i -= 1
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end
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# 選擇 coins[i]
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amt -= coins[i]
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count += 1
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end
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# 若未找到可行方案， 則返回 -1
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amt == 0 ? count : -1
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end
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### Driver Code ###
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if __FILE__ == $0
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# 貪婪：能夠保證找到全域性最優解
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coins = [1, 5, 10, 20, 50, 100]
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amt = 186
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res = coin_change_greedy(coins, amt)
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puts "\ncoins = #{coins}, amt = #{amt}"
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puts "湊到 #{amt} 所需的最少硬幣數量為 #{res}"
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# 貪婪：無法保證找到全域性最優解
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coins = [1, 20, 50]
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amt = 60
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res = coin_change_greedy(coins, amt)
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puts "\ncoins = #{coins}, amt = #{amt}"
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puts "湊到 #{amt} 所需的最少硬幣數量為 #{res}"
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puts "實際上需要的最少數量為 3 , 即 20 + 20 + 20"
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# 貪婪：無法保證找到全域性最優解
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coins = [1, 49, 50]
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amt = 98
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res = coin_change_greedy(coins, amt)
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puts "\ncoins = #{coins}, amt = #{amt}"
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puts "湊到 #{amt} 所需的最少硬幣數量為 #{res}"
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puts "實際上需要的最少數量為 2 , 即 49 + 49"
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end
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