Rearrange a linked list such that all even and odd positioned nodes are together - GeeksforGeeks

02 Nov, 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 nodesThe below program maintains two pointers ‘odd’ and ‘even’ for current nodes at odd and even positions respectively. We also store the first node of even linked list so that we can attach the even list at the end of odd list after all odd and even nodes are connected together in two different lists.  
C++
C
Java
Python3
C#
Javascript
// C++ program to rearrange a linked list in such a// way that all odd positioned node are stored before// all even positioned nodes#include<bits/stdc++.h>using namespace std; // Linked List Nodeclass Node{    public:    int data;    Node* next;}; // A utility function to create a new nodeNode* 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.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)    {        // If there are no more nodes, then connect        // first node of even list to the last node        // of odd list        if (!odd || !even || !(even->next))        {            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 listvoid printlist(Node * node){    while (node != NULL)    {        cout << node->data << "->";        node = node->next;    }    cout << "NULL" << endl;} // Driver codeint main(void){    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);     cout << "Given Linked List\n";    printlist(head);     head = rearrangeEvenOdd(head);     cout << "Modified Linked List\n";    printlist(head);     return 0;} // This is code is contributed by rathbhupendra
// C program to rearrange a linked list in such a// way that all odd positioned node are stored before// all even positioned nodes#include<bits/stdc++.h>using namespace std; // Linked List Nodestruct Node{    int data;    struct Node* next;}; // A utility function to create a new nodeNode* 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.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)    {        // If there are no more nodes, then connect        // first node of even list to the last node        // of odd list        if (!odd || !even || !(even->next))        {            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 listvoid printlist(Node * node){    while (node != NULL)    {        cout << node->data << "->";        node = node->next;    }    cout << "NULL" << endl;} // Driver codeint main(void){    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);     cout << "Given Linked List\n";    printlist(head);     head = rearrangeEvenOdd(head);     cout << "\nModified Linked List\n";    printlist(head);     return 0;}
// Java program to rearrange a linked list// in such a way that all odd positioned // node are stored before all even positioned nodesclass GfG{ // Linked List Nodestatic class Node{    int data;    Node next;} // A utility function to create a new nodestatic 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 liststatic void printlist(Node node){    while (node != null)    {        System.out.print(node.data + "->");        node = node.next;    }    System.out.println("NULL") ;} // Driver codepublic 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
# Python3 program to rearrange a linked list# in such a way that all odd positioned# node are stored before all even positioned nodes # Linked List Nodeclass Node:    def __init__(self, d):        self.data = d        self.next = None class LinkedList:    def __init__(self):        self.head = None             # A utility function to create    # a new node    def newNode(self, key):        temp = Node(key)        self.next = None        return temp     # Rearranges given linked list    # such that all even positioned    # nodes are before odd positioned.    # Returns new head of linked List.    def rearrangeEvenOdd(self, head):                 # Corner case        if (self.head == None):            return None         # Initialize first nodes of        # even and odd lists        odd = self.head        even = self.head.next         # Remember the first node of even list so        # that we can connect the even list at the        # end of odd list.        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 == None or even == None or                              (even.next) == None):                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 == None):                even.next = None                odd.next = evenFirst                break             # Connecting even nodes            even.next = odd.next            even = odd.next        return head     # A utility function to print a linked list    def printlist(self, node):        while (node != None):            print(node.data, end = "")            print("->", end = "")            node = node.next        print ("NULL")             # Function to insert a new node    # at the beginning    def push(self, new_data):        new_node = Node(new_data)        new_node.next = self.head        self.head = new_node # Driver codell = LinkedList()ll.push(5)ll.push(4)ll.push(3)ll.push(2)ll.push(1)print ("Given Linked List")ll.printlist(ll.head) start = ll.rearrangeEvenOdd(ll.head) print ("\nModified Linked List")ll.printlist(start) # This code is contributed by Prerna Saini
// C# program to rearrange a linked list// in such a way that all odd positioned// node are stored before all even positioned nodesusing System; class GfG{     // Linked List Node    class Node    {        public int data;        public 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)        {            Console.Write(node.data + "->");            node = node.next;        }        Console.WriteLine("NULL") ;    }     // Driver code    public static void Main()    {        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);         Console.WriteLine("Given Linked List");        printlist(head);         head = rearrangeEvenOdd(head);         Console.WriteLine("Modified Linked List");        printlist(head);    }} /* This code is contributed PrinciRaj1992 */
<script> // Javascript program to rearrange a linked list// in such a way that all odd positioned // node are stored before all even positioned nodes     // Linked List Node     class Node {            constructor() {                this.data = 0;                this.next = null;            }        }    // A utility function to create a new node    function newNode(key) {var 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.    function rearrangeEvenOdd(head) {        // Corner case        if (head == null)            return null;         // Initialize first nodes of even and        // odd listsvar odd = head;var even = head.next;         // Remember the first node of even list so        // that we can connect the even list at the        // end of odd list.var 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    function printlist(node) {        while (node != null) {            document.write(node.data + "->");            node = node.next;        }        document.write("NULL<br/>");    }     // Driver code     var 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);         document.write("Given Linked List<br/>");        printlist(head);         head = rearrangeEvenOdd(head);         document.write("Modified Linked List<br/>");        printlist(head); // This code contributed by gauravrajput1 </script>
Output: 
Given Linked List
1->2->3->4->5->NULL
Modified Linked List
1->3->5->2->4->NULL
 
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This article is contributed by Harsh Parikh.Please see here another code contributed by Gautam Singh.If you like GeeksforGeeks and would like to contribute, you can also write an article and mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above 
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