用于扁平化链接列表的 Javascript 程序

给定一个链表，其中每个节点都表示一个链表并包含其类型的两个指针：

1. 指向主列表中下一个节点的指针（我们在下面的代码中称其为“右”指针）。
2. 指向该节点指向的链表的指针（我们在下面的代码中将其称为“向下”指针）。

所有链表都已排序。请参阅以下示例

5 -> 10 -> 19 -> 28
       |    |     |     |
       V    V     V     V
       7    20    22    35
       |          |     |
       V          V     V
       8          50    40
       |                |
       V                V
       30               45

编写一个函数flatten() 将列表展平为单个链表。扁平化的链表也应该排序。比如上面的输入列表，输出列表应该是5->7->8->10->19->20->22->28->30->35->40->45->50 .

这个想法是对链表使用合并排序的 Merge() 过程。我们使用 merge() 来一个一个地合并列表。我们递归地合并（）当前列表与已经展平的列表。
向下指针用于链接展平列表的节点。

下面是上述方法的实现：

Javascript

// Javascript program for flattening 
// a Linked List
  
// Head of list
var head; 
  
// Linked list Node 
class Node 
{
    constructor(val) 
    {
        this.data = val;
        this.down = null;
        this.next = null;
    }
}
  
// An utility function to merge 
// two sorted linked lists
function merge(a, b) 
{
    // If first linked list is 
    // empty then second is the 
    // answer
    if (a == null)
    return b;
  
    // If second linked list is 
    // empty then first is the 
    // result
    if (b == null)
        return a;
  
    // Compare the data members of 
    // the two linked lists and put 
    // the larger one in the result
    var result;
  
    if (a.data < b.data) 
    {
        result = a;
        result.down = merge(a.down, b);
    }
  
    else 
    {
        result = b;
        result.down = merge(a, b.down);
    }
  
    result.right = null;
    return result;
}
  
function flatten(root) 
{
    // Base Cases
    if (root == null || 
        root.right == null)
        return root;
  
    // Recur for list on right
    root.right = flatten(root.right);
  
    // Now merge
    root = merge(root, root.right);
  
    // Return the root
    // It will be in turn merged
    // with its left
    return root;
}
  
/* Utility function to insert a node 
   at beginning of the linked list */
function push(head_ref, data) 
{
    /* 1 & 2: Allocate the Node & 
              Put in the data */
         var new_node = new Node(data);
  
    // 3. Make next of new Node as head
    new_node.down = head_ref;
  
    // 4. Move the head to point to 
    // new Node 
    head_ref = new_node;
  
    // 5. return to link it back 
        return head_ref;
}
  
function printList() 
{
    var temp = head;
    while (temp != null) 
    {
        document.write(temp.data + " ");
        temp = temp.down;
    }
    document.write();
}
  
// Driver code
/* Create the following linked list 
   5 -> 10 -> 19 -> 28 | | | | V V V 
   V 7 20 22 35 | | | V V V 8 50 40 
   | | V V 30 45 */
head = push(head, 30);
head = push(head, 8);
head = push(head, 7);
head = push(head, 5);
  
head.right = push(head.right, 20);
head.right = push(head.right, 10);
  
head.right.right = 
push(head.right.right, 50);
head.right.right = 
push(head.right.right, 22);
head.right.right = 
push(head.right.right, 19);
  
head.right.right.right = 
push(head.right.right.right, 45);
head.right.right.right = 
push(head.right.right.right, 40);
head.right.right.right = 
push(head.right.right.right, 35);
head.right.right.right = 
push(head.right.right.right, 20);
  
// Flatten the list
head = flatten(head);
  
printList();
// This code is contributed by aashish1995 

输出：

5 7 8 10 19 20 20 22 30 35 40 45 50

有关详细信息，请参阅有关扁平化链接列表的完整文章！