調試基本的ruby遞歸

Question

該代碼旨在獲取一個整數硬幣值數組，一個要進行的零錢交易以及一個空數組以收集答案，並且應該返回一組硬幣，這些硬幣可以進行正確的零錢兌換（假設問題是可能的）。

從puts語句來看，似乎遞歸表現良好並且正在尋找正確的答案，但是返回的解決方案不是有效的答案。 有人可以讓我知道我在做什么錯嗎？

我的代碼：

    def brute_solver(coins,amount,answer)
        puts "Coins: #{coins}, Amount: #{amount}, Answer: #{answer}"
        return answer.sort! if amount == 0
        coins.each do |c|
            brute_solver(coins, amount - c, answer.dup << c) unless amount - c < 0
        end 
    end

運行brute_solver的示例嘗試：

    1.9.3p194 :001 > require './change_challenge.rb'
     => true 
    1.9.3p194 :002 > brute_solver([1,3,5],7,[])
    Coins: [1, 3, 5], Amount: 7, Answer: []
    Coins: [1, 3, 5], Amount: 6, Answer: [1]
    Coins: [1, 3, 5], Amount: 5, Answer: [1, 1]
    Coins: [1, 3, 5], Amount: 4, Answer: [1, 1, 1]
    Coins: [1, 3, 5], Amount: 3, Answer: [1, 1, 1, 1]
    Coins: [1, 3, 5], Amount: 2, Answer: [1, 1, 1, 1, 1]
    Coins: [1, 3, 5], Amount: 1, Answer: [1, 1, 1, 1, 1, 1]
    Coins: [1, 3, 5], Amount: 0, Answer: [1, 1, 1, 1, 1, 1, 1]
    Coins: [1, 3, 5], Amount: 0, Answer: [1, 1, 1, 1, 3]
    Coins: [1, 3, 5], Amount: 1, Answer: [1, 1, 1, 3]
    Coins: [1, 3, 5], Amount: 0, Answer: [1, 1, 1, 3, 1]
    Coins: [1, 3, 5], Amount: 2, Answer: [1, 1, 3]
    Coins: [1, 3, 5], Amount: 1, Answer: [1, 1, 3, 1]
    Coins: [1, 3, 5], Amount: 0, Answer: [1, 1, 3, 1, 1]
    Coins: [1, 3, 5], Amount: 0, Answer: [1, 1, 5]
    Coins: [1, 3, 5], Amount: 3, Answer: [1, 3]
    Coins: [1, 3, 5], Amount: 2, Answer: [1, 3, 1]
    Coins: [1, 3, 5], Amount: 1, Answer: [1, 3, 1, 1]
    Coins: [1, 3, 5], Amount: 0, Answer: [1, 3, 1, 1, 1]
    Coins: [1, 3, 5], Amount: 0, Answer: [1, 3, 3]
    Coins: [1, 3, 5], Amount: 1, Answer: [1, 5]
    Coins: [1, 3, 5], Amount: 0, Answer: [1, 5, 1]
    Coins: [1, 3, 5], Amount: 4, Answer: [3]
    Coins: [1, 3, 5], Amount: 3, Answer: [3, 1]
    Coins: [1, 3, 5], Amount: 2, Answer: [3, 1, 1]
    Coins: [1, 3, 5], Amount: 1, Answer: [3, 1, 1, 1]
    Coins: [1, 3, 5], Amount: 0, Answer: [3, 1, 1, 1, 1]
    Coins: [1, 3, 5], Amount: 0, Answer: [3, 1, 3]
    Coins: [1, 3, 5], Amount: 1, Answer: [3, 3]
    Coins: [1, 3, 5], Amount: 0, Answer: [3, 3, 1]
    Coins: [1, 3, 5], Amount: 2, Answer: [5]
    Coins: [1, 3, 5], Amount: 1, Answer: [5, 1]
    Coins: [1, 3, 5], Amount: 0, Answer: [5, 1, 1]
     => [1, 3, 5] 

Answer 1

def brute_solver(coins,amount,answer)

        puts "Coins: #{coins}, Amount: #{amount}, Answer: #{answer}"

        return answer.sort! if amount == 0

        coins.each do |c|
            if amount - c < 0
                break
            end
            result = brute_solver(coins, amount - c, answer.dup << c)
            if result != -1
                return result
            end
        end 
        return -1

end

puts brute_solver([5, 7],26,[])

這樣，如果找到正確的解決方案，函數將返回一個數組，否則返回-1。 進行遞歸調用時，您還返回遞歸找到的解決方案（如果返回值不為-1，則表示找到了解決方案）

您的代碼不起作用，因為在ruby中某個函數的返回值是最后執行的語句，並且即使找到硬幣的有效組合，您的函數仍會繼續執行命令。 基本上，您的函數返回它檢查過的硬幣的最后組合，以查看它們是否為解決方案。