用于反转双向链表的 Javascript 程序

给定一个双向链表，任务是反转给定的双向链表。

例如，请参见下图。

(a) Original Doubly Linked List  

(b) Reversed Doubly Linked List  

这是一个反转双向链表的简单方法。我们需要做的就是交换所有节点的 prev 和 next 指针，更改 head（或 start）的 prev 并最终更改 head 指针。

Javascript

// Javascript program to reverse a 
// doubly linked list
var head;
  
class Node 
{
    constructor(val) 
    {
        this.data = val;
        this.prev = null;
        this.next = null;
    }
}
      
/* Function to reverse a Doubly Linked List */
function reverse() 
{
    var temp = null;
    var current = head;
      
    /* Swap next and prev for all nodes of
       doubly linked list */
    while (current != null) 
    {
        temp = current.prev;
        current.prev = current.next;
        current.next = temp;
        current = current.prev;
    }
  
    /* Before changing head, check for the cases 
       like empty list and list with only one node */
    if (temp != null) 
    {
        head = temp.prev;
    }
}
  
// UTILITY FUNCTIONS 
/* Function to insert a node at the beginning 
   of the Doubly Linked List */
function push(new_data) 
{
    // Allocate node 
    var new_node = new Node(new_data);
     
    /* Since we are adding at the beginning, 
       prev is always NULL */
    new_node.prev = null;
  
    /* Link the old list off the new node */
    new_node.next = head;
  
    /* Change prev of head node to new node */
    if (head != null) 
    {
        head.prev = new_node;
    }
  
    /* Move the head to point to the new node */
    head = new_node;
}
  
/* Function to print nodes in a given doubly 
   linked list This function is same as 
   printList() of singly linked list */
function printList(node) 
{
    while (node != null) 
    {
        document.write(node.data + " ");
        node = node.next;
    }
}
  
/* Let us create a sorted linked list to test 
   the functions Created linked list will be 
   10->8->4->2 */
push(2);
push(4);
push(8);
push(10);
  
document.write(
"Original linked list <br/>");
printList(head);
  
reverse();
document.write("<br/>");
document.write("The reversed Linked List is <br/>");
printList(head);
// This code is contributed by gauravrajput1

输出：

Original linked list 
10 8 4 2 
The reversed Linked List is 
2 4 8 10

方法二：

同样的问题也可以通过使用 Stacks 来完成。

脚步：

1. 继续将节点的数据推入堆栈。 -> O(n)
2. 不断弹出元素并更新双向链表

Javascript

// Javascript program to reverse a doubly 
// linked list
class Node 
{
    constructor(d)
    {
        this.data = d;
        this.next = this.prev = null;
    }
}
  
let head;
  
// Function to reverse a Doubly 
// Linked List using Stacks
function reverse()
{
    let stack = [];
    let temp = head;
      
    while (temp != null)
    {
        stack.push(temp.data);
        temp = temp.next;
    }
      
    // Added all the elements sequence 
    // wise in the stack
    temp = head;
      
    while (temp != null)
    {
        temp.data = stack.pop();
        temp = temp.next;
    }
      
    // Popped all the elements and the 
    // added in the linked list,
    // which are in the reversed order.
}
  
// UTILITY FUNCTIONS 
// Function to insert a node at the 
// beginning of the Doubly Linked List 
function push(new_data)
{
      
    // Allocate node 
    let new_node = new Node(new_data);
  
    /* Since we are adding at the beginning,
       prev is always NULL */
    new_node.prev = null;
  
    // Link the old list off the new node 
    new_node.next = head;
  
    /* Change prev of head node to 
       new node */
    if (head != null) 
    {
        head.prev = new_node;
    }
  
    // Move the head to point to the 
    // new node 
    head = new_node;
}
  
// Function to print nodes in a given 
// doubly linked list. This function
// is same as printList() of singly
// linked list
function printList(node)
{
    while (node != null) 
    {
        document.write(node.data + " ");
        node = node.next;
    }
}
  
// Driver Code
  
// Let us create a sorted linked list 
// to test the functions Created linked
// list will be 10->8->4->2
push(2);
push(4);
push(8);
push(10);
  
document.write(
"Original linked list <br>");
printList(head);
  
reverse();
document.write("<br>");
document.write(
"The reversed Linked List is <br>");
printList(head);
// This code is contributed by rag2127

输出：

Original linked list 
10 8 4 2 
The reversed Linked List is 
2 4 8 10

时间复杂度： O(N)
辅助空间： O(N)

在这个方法中，我们遍历链表一次并将元素添加到堆栈中，然后再次遍历整体以更新所有元素。整体需要2n时间，也就是O(n)的时间复杂度。

有关详细信息，请参阅有关反向双向链表的完整文章！