How can I implement a merge sort algorithm for a doubly linked list in Java?

Answer 1

To implement a merge sort algorithm for a doubly linked list in Java, you can follow these steps:

1. Divide the doubly linked list into two halves.
2. Recursively sort each half using merge sort.
3. Merge the two sorted halves back together in sorted order.

You can achieve this by creating a mergeSort() method that takes the doubly linked list as input and recursively divides and merges the list. Make sure to handle the merging process for doubly linked lists by adjusting the pointers accordingly.

Here is a basic outline of how you can implement this algorithm in Java:

java public class MergeSortDoublyLinkedList

public Node mergeSort(Node head) 
    if (head  null  head.next  null) 
        return head;
    
    
    Node middle  getMiddle(head);
    Node nextOfMiddle  middle.next;
    
    middle.next  null;
    
    Node left  mergeSort(head);
    Node right  mergeSort(nextOfMiddle);
    
    return merge(left, right);


private Node merge(Node left, Node right) 
    if (left  null) 
        return right;
    
    if (right  null) 
        return left;
    
    
    Node result  null;
    
    if (left.data  right.data) 
        result  left;
        result.next  merge(left.next, right);
        result.next.prev  result;
     else 
        result  right;
        result.next  merge(left, right.next);
        result.next.prev  result;
    
    
    return result;


private Node getMiddle(Node head) 
    if (head  null) 
        return head;
    
    
    Node slow  head;
    Node fast  head;
    
    while (fast.next ! null  fast.next.next ! null) 
        slow  slow.next;
        fast  fast.next.next;
    
    
    return slow;


class Node 
    int data;
    Node prev;
    Node next;
    
    public Node(int data) 
        this.data  data;
    

This code snippet provides a basic implementation of the merge sort algorithm for a doubly linked list in Java. You can further customize and optimize it based on your specific requirements.