JavaScript数据结构之双向链表和双向循环链表的实(2)

/*双向循环链表*/ 
function DoublyCircularLinkedList(){ 
  var Node = function(element){ 
    this.element = element; 
    this.next = null; 
    this.prev = null; 
  }; 
 
  var length = 0, 
    head = null, 
    tail = null; 
 
  this.append = function(element){ 
    var node = new Node(element), 
      current, 
      previous; 
 
    if (!head) { 
      head = node; 
      tail = node; 
      head.prev = tail; 
      tail.next = head; 
    }else{ 
      current = head; 
 
      while(current.next !== head){ 
        previous = current; 
        current = current.next; 
      } 
 
      current.next = node; 
      node.next = head; 
      node.prev = current; 
    }; 
 
    length++; 
    return true; 
  }; 
 
  this.insert = function(position, element){ 
    if(position >= 0 && position <= length){ 
      var node = new Node(element), 
        index = 0, 
        current = head, 
          previous; 
 
      if(position === 0){ 
         
        if(!head){ 
 
          node.next = node; 
          node.tail = node; 
          head = node; 
          tail = node; 
 
        }else{ 
 
          current.prev = node; 
          node.next = current; 
          head = node; 
          node.prev = tail; 
 
        } 
         
      }else if(position === length){ 
        current = tail; 
 
        current.next = node; 
        node.prev = current; 
        tail = node; 
        node.next = head; 
      }else{ 
 
        while(index++ < position){ 
          previous = current; 
          current = current.next; 
        } 
 
        current.prev = node; 
        node.next = current; 
        previous.next = node; 
        node.prev = previous; 
 
      } 
 
      length++; 
      return true; 
    }else{ 
      return false; 
    } 
  }; 
 
  this.removeAt = function(position){ 
    if(position > -1 && position < length){ 
 
      var current = head, 
        index = 0, 
        previous; 
 
      if(position === 0){ 
 
        current.next.previous = tail; 
        head = current.next; 
 
      }else if(position === length - 1){ 
 
        current = tail; 
 
        current.prev.next = head; 
        head.prev = current.prev; 
        tail = current.prev; 
      }else{ 
 
        while(index++ < position){ 
          previous = current; 
          current = current.next; 
        } 
 
        previous.next = current.next; 
        current.next.prev = previous; 
 
      } 
 
      length--; 
      return true; 
    }else{ 
      return false; 
    } 
  }; 
 
  this.remove = function(element){ 
    var current = head, 
      previous, 
      indexCheck = 0; 
 
    while(current && indexCheck < length){ 
      if(current.element === element){ 
        if(indexCheck === 0){ 
          current.next.prev = tail; 
          head = current.next; 
        }else{ 
          current.next.prev = previous; 
          previous.next = current.next; 
        } 
        length--; 
        return true; 
      } 
 
      previous = current; 
      current = current.next; 
      indexCheck++; 
    } 
 
    return false; 
  }; 
 
  this.remove = function(){ 
    if(length === 0){ 
      return false; 
    } 
 
    var current = head, 
      previous, 
      indexCheck = 0; 
 
    if(length === 1){ 
      head = null; 
      tail = null; 
      length--; 
      return current.element; 
    } 
 
    while(indexCheck++ < length){ 
      previous = current; 
      current = current.next; 
    } 
 
    previous.next = head; 
    tail = previous.next; 
    length--; 
    return current.element; 
  }; 
 
  this.indexOf = function(element){ 
    var current = head, 
      index = 0; 
 
    while(current && index++ < length){ 
      if(current.element === element){ 
        return index; 
      } 
      current = current.next; 
    } 
 
    return false; 
  }; 
 
  this.toString = function(){ 
    var current = head, 
      indexCheck = 0, 
      string = ''; 
 
    while(current && indexCheck < length){ 
      string += current.element; 
      indexCheck++; 
      current = current.next; 
    }   
 
    return string; 
  }; 
 
  this.isEmpty = function(){ 
    return length === 0; 
  }; 
 
  this.getHead = function(){ 
    return head; 
  }; 
 
  this.getTail = function(){ 
    return tail; 
  }; 
 
  this.size = function(){ 
    return length; 
  }; 
}