Coding JAVA Linked List Merge Sort Searching and Sorting

Merge Sort for Doubly Linked List

JAVA Programming-Merge Sort for Doubly Linked List - Searching and Sorting - Merge sort for singly linked list is already discussed. The important change here is to modify the previous pointers also when merging two lists.

Given a doubly linked list, write a function to sort the doubly linked list in increasing order using merge sort.

For example, the following doubly linked list should be changed to 2<->4<->8<->10

The important change here is to modify the previous pointers also when merging two lists.

Doubly Linked List (DLL):

Doubly Linked List (DLL) is a list of elements and it varies from Linked List. It allows navigation, either forward or backward when compared to Single Linked List. It has two pointers: previous pointer and next pointer. Every element points to next of the list and previous element in list.

Terms used in doubly linked list:

  • Link
  • Next
  • Prev
  • Linked list
Doubly Linked List
Doubly Linked List

JAVA Programming Implementation of merge sort for doubly linked list:

Java


class LinkedList {
 
    static Node head;  
 
  
    static class Node {
 
        int data;
        Node next, prev;
 
      
        Node(int d) {
            data = d;
            next = prev = null;
        }
    }
 
    void print(Node node) {
        Node temp = node;
        System.out.println("Forward Traversal using next pointer");
        while (node != null) {
            System.out.print(node.data + " ");
            temp = node;
            node = node.next;
        }
        System.out.println("\nBackward Traversal using prev pointer");
        while (temp != null) {
            System.out.print(temp.data + " ");
            temp = temp.prev;
        }
    }
 
  
    Node split(Node head) {
        Node fast = head, slow = head;
        while (fast.next != null && fast.next.next != null) {
            fast = fast.next.next;
            slow = slow.next;
        }
        Node temp = slow.next;
        slow.next = null;
        return temp;
    }
 
    Node mergeSort(Node node) {
        if (node == null || node.next == null) {
            return node;
        }
        Node second = split(node);
 
        
        node = mergeSort(node);
        second = mergeSort(second);
 
        
        return merge(node, second);
    }
 
 
    Node merge(Node first, Node second) {
       
        if (first == null) {
            return second;
        }
 
       
        if (second == null) {
            return first;
        }
 
       
        if (first.data < second.data) {
            first.next = merge(first.next, second);
            first.next.prev = first;
            first.prev = null;
            return first;
        } else {
            second.next = merge(first, second.next);
            second.next.prev = second;
            second.prev = null;
            return second;
        }
    }
 
   
    public static void main(String[] args) {
 
        LinkedList list = new LinkedList();
        list.head = new Node(10);
        list.head.next = new Node(30);
        list.head.next.next = new Node(3);
        list.head.next.next.next = new Node(4);
        list.head.next.next.next.next = new Node(20);
        list.head.next.next.next.next.next = new Node(5);
         
         
        Node node = null;
        node = list.mergeSort(head);
        System.out.println("Linked list after sorting :");
        list.print(node);
 
    }
}
 

Output:

Linked List after sorting
Forward Traversal using next pointer
3 4 5 10 20 30
Backward Traversal using prev pointer
30 20 10 5 4 3

Time Complexity: Time complexity of the above implementation is same as time complexity of MergeSort for arrays. It takes Θ(nLogn) time.

READ  Iterative Quick Sort

About the author

Venkatesan Prabu

Venkatesan Prabu

Wikitechy Founder, Author, International Speaker, and Job Consultant. My role as the CEO of Wikitechy, I help businesses build their next generation digital platforms and help with their product innovation and growth strategy. I'm a frequent speaker at tech conferences and events.

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