Question

查看来自coursera的scala课程提供的资源，我发现了一个应该工作的算法（逻辑应该可行），但是当在scala中实现时，它会返回堆栈溢出。我想我知道堆栈是什么，因为我在C中玩了一段时间，但我不明白以下函数如何耗尽这么多内存：

      def countChange(money: Int, coins: List[Int]): Int = {


    def cc(amount: Int, list: List[Int]): Int = {
      if (amount == 0) 1
      if (amount < 0 || list.isEmpty) 0

      return cc(amount - list.head, list) + cc(amount, list.tail)

    }

    cc(money, coins)






  }

这是错误：

Exception in thread "main" java.lang.StackOverflowError
at java.lang.Integer.valueOf(Unknown Source)
at scala.runtime.BoxesRunTime.boxToInteger(BoxesRunTime.java:70)
at recfun.Main$.cc$1(Main.scala:78)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)
at recfun.Main$.cc$1(Main.scala:80)

这是对函数的调用：

 println ("" + countChange(10,List(2,3,5)))

Answer 1

错误的return行为（混合表达式和陈述）

没有return关键字：

def countChange(money: Int, coins: List[Int]): Int = {
  def cc(amount: Int, list: List[Int]): Int = {
    if (amount == 0) 1
    else if (amount < 0 || list.isEmpty) 0
    else cc(amount - list.head, list) + cc(amount, list.tail)
  }
  cc(money, coins)
}

或使用return关键字：

def countChange1(money: Int, coins: List[Int]): Int = {
  def cc(amount: Int, list: List[Int]): Int = {
    if (amount == 0) return 1
    if (amount < 0 || list.isEmpty) return 0
    return cc(amount - list.head, list) + cc(amount, list.tail)
  }
  cc(money, coins)
}

scala中的堆栈溢出递归更改硬币函数

1 个答案: