JavaScript双向链表和双向循环链表的实现

双向链表和普通链表的区别在于，在链表中，一个节点只有链向下一个节点的链接，而在双向链表中，链接是双向的：一个链向下一个元素，另一个链向前一个元素。 双向链表提供了两种迭代列表的方法：从头到尾，或者反过来。我们也可以访问一个特定节点的下一个或前一个元素。在单向链表中，如果迭代列表时错过了要找的元素，就需要回到列表起点，重新开始迭代。这是双向链表的一个优点。本文主要介绍JavaScript数据结构之双向链表和双向循环链表的实现。

双向链表：单向链表只能向着一个方向遍历链表节点，而在节点指针域中增加了前向指针的双向链表，则可以向着两个方向遍历节点。这使得双向链表也可以在任何一个节点遍历整个链表。

function DoublyLinkedList() { 
  var Node = function(element) { 
    this.element = element; 
    this.next = null; 
    this.prev = null; 
  }; 
 
  var length = 0, 
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    tail = null; 
 
  this.append = function(element){ 
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    length++; 
    return true; 
  } 
 
  this.insert = function(position,element){ 
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      length++; 
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    }else{ 
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    } 
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  this.removeAt = function(position){ 
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      if (position === 0) { 
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      } else{ 
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    } 
    return string; 
  }; 
 
  this.getHead = function(){ 
    return head; 
  }; 
 
  this.getTail = function(){ 
    return tail; 
  }; 
}

双向循环链表：将双向链表的头尾指针相连，就构成了双向循环链表。这种链表从任意一个节点都可以同时向两个方向进行节点遍历，查询节点的速度也是最快的。

/*双向循环链表*/ 
function DoublyCircularLinkedList(){ 
  var Node = function(element){ 
    this.element = element; 
    this.next = null; 
    this.prev = null; 
  }; 
 
  var length = 0, 
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  this.append = function(element){ 
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      node.next = head; 
      node.prev = current; 
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    length++; 
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  this.insert = function(position, element){ 
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  this.removeAt = function(position){ 
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    previous.next = head; 
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  this.indexOf = function(element){ 
    var current = head, 
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    while(current && index++ < length){ 
      if(current.element === element){ 
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      current = current.next; 
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  this.toString = function(){ 
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  this.isEmpty = function(){ 
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  this.getHead = function(){ 
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  }; 
 
  this.getTail = function(){ 
    return tail; 
  }; 
 
  this.size = function(){ 
    return length; 
  }; 
}

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