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Java Program For Rearranging A Linked List Such That All Even And Odd Positioned Nodes Are Together

  • Last Updated : 30 Dec, 2021

Rearrange a linked list in such a way that all odd position nodes are together and all even positions node are together, 
Examples: 

Input:   1->2->3->4
Output:  1->3->2->4

Input:   10->22->30->43->56->70
Output:  10->30->56->22->43->70

The important thing in this question is to make sure that all below cases are handled 

  1. Empty linked list.
  2. A linked list with only one node.
  3. A linked list with only two nodes.
  4. A linked list with an odd number of nodes.
  5. A linked list with an even number of nodes.

The below program maintains two pointers ‘odd’ and ‘even’ for current nodes at odd and even positions respectively. We also store the first node of the even linked list so that we can attach the even list at the end of the odd list after all odd and even nodes are connected together in two different lists.

Java




// Java program to rearrange a linked list 
// in such a way that all odd positioned  
// node are stored before all even 
// positioned nodes 
class GfG { 
  
// Linked List Node 
static class Node 
    int data; 
    Node next; 
}
  
// A utility function to create 
// a new node 
static Node newNode(int key) 
    Node temp = new Node(); 
    temp.data = key; 
    temp.next = null
    return temp; 
  
// Rearranges given linked list 
// such that all even positioned 
// nodes are before odd positioned. 
// Returns new head of linked List. 
static Node rearrangeEvenOdd(Node head) 
    // Corner case 
    if (head == null
        return null
  
    // Initialize first nodes of even 
    // and odd lists 
    Node odd = head; 
    Node even = head.next; 
  
    // Remember the first node of even 
    // list so that we can connect the 
    // even list at the end of odd list. 
    Node evenFirst = even; 
  
    while (1 == 1
    
        // If there are no more nodes,  
        // then connect first node of even  
        // list to the last node of odd list 
        if (odd == null || even == null ||
           (even.next) == null
        
            odd.next = evenFirst; 
            break
        
  
        // Connecting odd nodes 
        odd.next = even.next; 
        odd = even.next; 
  
        // If there are NO more even 
        // nodes after current odd. 
        if (odd.next == null
        
            even.next = null
            odd.next = evenFirst; 
            break
        
  
        // Connecting even nodes 
        even.next = odd.next; 
        even = odd.next; 
    
    return head; 
  
// A utility function to print 
// a linked list 
static void printlist(Node node) 
    while (node != null
    
        System.out.print(node.data + "->"); 
        node = node.next; 
    
    System.out.println("NULL") ; 
  
// Driver code 
public static void main(String[] args) 
    Node head = newNode(1); 
    head.next = newNode(2); 
    head.next.next = newNode(3); 
    head.next.next.next = newNode(4); 
    head.next.next.next.next = newNode(5); 
  
    System.out.println("Given Linked List"); 
    printlist(head); 
  
    head = rearrangeEvenOdd(head); 
  
    System.out.println("Modified Linked List"); 
    printlist(head); 
}
// This code is contributed by Prerna saini

Output: 

Given Linked List
1->2->3->4->5->NULL
Modified Linked List
1->3->5->2->4->NULL

Please refer complete article on Rearrange a linked list such that all even and odd positioned nodes are together for more details!


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