循环迭代

问题描述

我需要遍历一个List，但要循环遍历.我也需要向列表中添加新元素并遍历所有元素(旧元素和新闻元素)，我该怎么做?有没有适合他们的数据结构?

I need iterate through a List but circular way. I need too add new elements to the list and iterate over all elements (olds and news elements), How I do it? Is there any data structure for them?

推荐答案

我认为这可能就是您想要的；甚至在迭代过程中也可以向列表中添加新元素的功能.代码很丑陋，但似乎可以正常工作.

I think maybe this is what you want; the ability to add new elements to your list even as you are iterating it. The code is ugly but it seems to work.

import scala.collection.mutable.Queue

class Circular[A](list: Seq[A]) extends Iterator[A]{

  val elements = new Queue[A] ++= list
  var pos = 0

  def next = {
    if (pos == elements.length)
      pos = 0
    val value = elements(pos)
    pos = pos + 1
    value
  }

  def hasNext = !elements.isEmpty
  def add(a: A): Unit = { elements += a }
  override def toString = elements.toString

}

您可以像这样使用它:

scala> var circ = new Circular(List(1,2))
res26: Circular[Int] = Queue(1,2)
scala> circ.next
res27: Int = 1
scala> circ.next
res28: Int = 2
scala> circ.next
res29: Int = 1
scala> circ.add(5)
scala> circ.next
res30: Int = 2
scala> circ.next
res31: Int = 5
scala> circ
res32: Circular[Int] = Queue(1,2,5)

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