Find extra node in the second Linked list

Given two Linked list L1 and L2. The second list L2 contains all the nodes of L1 along with 1 extra node. The task is to find that extra node. 
Examples:

Input: L1 = 17 -> 7 -> 6 -> 16 
L2 = 17 -> 7 -> 6 -> 16 -> 15 
Output: 15 
Explanation:
Element 15 is not present in the L1 list
Input: L1 = 10 -> 15 -> 5 
L2 = 10 -> 100 -> 15 -> 5 
Output: 100 

Naive approach:

• Run nested loops and find the nodes in L2 which is not present in L1. 
  
• The time complexity of this approach will be O(N²) where N is the length of the linked list. 
  

Efficient approach:

• If all the nodes of the L1 and L2 are XORed together then every node of A[] will give 0 with its occurrence in L2 and the extra element say X when XORed with 0 will give (X XOR 0) = X which is the result. 
  

Below is the implementation of the above approach:

C++

// C++ program to find the
// extra node
#include <bits/stdc++.h>

using namespace std;

// Node of the singly linked
// list
struct Node {
    int data;
    Node* next;
};

// Function to insert a node at
// the beginning of the singly
// Linked List
void push(Node** head_ref,
          int new_data)
{
    // allocate node
    Node* new_node =
    (Node*)malloc(sizeof
                  (struct Node));

    // put in the data
    new_node->data = new_data;

    // link the old list of the
    // new node
    new_node->next = (*head_ref);

    // move the head to point to
    // the new node
    (*head_ref) = new_node;
}

int print(Node* head_ref,
          Node* head_ref1)
{
    int ans = 0;

    Node* ptr1 = head_ref;
    Node* ptr2 = head_ref1;
    // Traverse the linked list
    while (ptr1 != NULL) {
        ans ^= ptr1->data;
        ptr1 = ptr1->next;
    }
    while (ptr2 != NULL) {
        ans ^= ptr2->data;
        ptr2 = ptr2->next;
    }
    return ans;
}

// Driver program
int main()
{
    // start with the empty list
    Node* head1 = NULL;
    Node* head2 = NULL;
    // create the linked list
    // 15 -> 16 -> 7 -> 6 -> 17
    push(&head1, 17);
    push(&head1, 7);
    push(&head1, 6);
    push(&head1, 16);

    // second  LL
    push(&head2, 17);
    push(&head2, 7);
    push(&head2, 6);
    push(&head2, 16);
    push(&head1, 15);
    int k = print(head1, head2);
    cout << k;
    return 0;
}

Java

// Java program to find the
// extra node
class GFG {
    // Node of the singly
    // linked list
    static class Node {
        int data;
        Node next;
    };

    // Function to insert a node at
    // the beginning of the singly
    // Linked List
    static Node push(Node head_ref,
                     int new_data)
    {
        // allocate node
        Node new_node = new Node();

        // put in the data
        new_node.data = new_data;

        // link the old list off
        // the new node
        new_node.next = (head_ref);

        // move the head to point
        // to the new node
        (head_ref) = new_node;
        return head_ref;
    }

    static void extra(Node head_ref1,
                      Node head_ref2)
    {
        int ans = 0;

        Node ptr1 = head_ref1;
        Node ptr2 = head_ref2;

        // Traverse the linked list
        while (ptr1 != null) {
            ans ^= ptr1.data;
            ptr1 = ptr1.next;
        }
        while (ptr2 != null) {
            ans ^= ptr2.data;
            ptr2 = ptr2.next;
        }

        System.out.println(ans);
    }

    // Driver code
    public static void main(String args[])
    {
        // start with the empty list
        Node head1 = null;
        Node head2 = null;
        // create the linked list
        // 15 . 16 . 7 . 6 . 17
        head1 = push(head1, 17);
        head1 = push(head1, 7);
        head1 = push(head1, 6);
        head1 = push(head1, 16);
        head1 = push(head1, 15);

        // second LL
        head2 = push(head2, 17);
        head2 = push(head2, 7);
        head2 = push(head2, 6);
        head2 = push(head2, 16);

        extra(head1, head2);
    }
}

Python3

# Python3 program to find the
# extra node
class Node:

    def __init__(self, data):
        self.data = data
        self.next = next

# Function to insert a node at
# the beginning of the singly
# Linked List
def push( head_ref, new_data) :

    # allocate node
    new_node = Node(0)

    # put in the data
    new_node.data = new_data

    # link the old list off
    # the new node
    new_node.next = (head_ref)

    # move the head to point
    # to the new node
    (head_ref) = new_node
    return head_ref


def extra(head_ref1, head_ref2) :

    ans = 0

    ptr1 = head_ref1
    ptr2 = head_ref2
    # Traverse the linked list
    while (ptr1 != None):
        # if current node is prime,
        # Find sum and product
        ans ^= ptr1.data
        ptr1 = ptr1.next
    while(ptr2 != None):
        ans^= ptr2.data
        ptr2 = ptr2.next
    print(ans)
   ## print( "Product = ", prod)

# Driver code

# start with the empty list
head1 = None
head2 = None
# create the linked list
# 15 . 16 . 7 . 6 . 17
head1 = push(head1, 17)
head1 = push(head1, 7)
head1 = push(head1, 6)
head1 = push(head1, 16)
head1 = push(head1, 15)

# create the linked list
head2 = push(head2, 17)
head2 = push(head2, 7)
head2 = push(head2, 6)
head2 = push(head2, 16)


extra(head1, head2)

C#

// C# program to find the extra node
using System;

class GFG{

// Node of the singly
// linked list
class Node
{
    public int data;
    public Node next;
};

// Function to insert a node at
// the beginning of the singly
// Linked List
static Node push(Node head_ref,
                 int new_data)
{

    // Allocate node
    Node new_node = new Node();

    // Put in the data
    new_node.data = new_data;

    // Link the old list off
    // the new node
    new_node.next = (head_ref);

    // Move the head to point
    // to the new node
    (head_ref) = new_node;

    return head_ref;
}

static void extra(Node head_ref1,
                  Node head_ref2)
{
    int ans = 0;

    Node ptr1 = head_ref1;
    Node ptr2 = head_ref2;

    // Traverse the linked list
    while (ptr1 != null)
    {
        ans ^= ptr1.data;
        ptr1 = ptr1.next;
    }
    while (ptr2 != null)
    {
        ans ^= ptr2.data;
        ptr2 = ptr2.next;
    }
    Console.WriteLine(ans);
}

// Driver code
public static void Main(String []args)
{

    // Start with the empty list
    Node head1 = null;
    Node head2 = null;

    // Create the linked list
    // 15 . 16 . 7 . 6 . 17
    head1 = push(head1, 17);
    head1 = push(head1, 7);
    head1 = push(head1, 6);
    head1 = push(head1, 16);
    head1 = push(head1, 15);

    // Second LL
    head2 = push(head2, 17);
    head2 = push(head2, 7);
    head2 = push(head2, 6);
    head2 = push(head2, 16);

    extra(head1, head2);
}
}

// This code is contributed by Rajput-Ji

Javascript

<script>

// Javascript program to find the
// extra node

// Node of the singly linked
// list
class Node {

    constructor()
    {
        this.data = 0;
        this.next = null;
    }
};

// Function to insert a node at
// the beginning of the singly
// Linked List
function push(head_ref, new_data)
{
    // allocate node
    var new_node = new Node();

    // put in the data
    new_node.data = new_data;

    // link the old list of the
    // new node
    new_node.next = (head_ref);

    // move the head to point to
    // the new node
    (head_ref) = new_node;
    return head_ref;
}

function print(head_ref, head_ref1)
{
    var ans = 0;

    var ptr1 = head_ref;
    var ptr2 = head_ref1;
    // Traverse the linked list
    while (ptr1 != null) {
        ans ^= ptr1.data;
        ptr1 = ptr1.next;
    }
    while (ptr2 != null) {
        ans ^= ptr2.data;
        ptr2 = ptr2.next;
    }
    return ans;
}

// Driver program
// start with the empty list
var head1 = null;
var head2 = null;

// create the linked list
// 15 . 16 . 7 . 6 . 17
head1 = push(head1, 17);
head1 = push(head1, 7);
head1 = push(head1, 6);
head1 = push(head1, 16);

// second  LL
head2 = push(head2, 17);
head2 = push(head2, 7);
head2 = push(head2, 6);
head2 = push(head2, 16);
head1 = push(head1, 15);
var k = print(head1, head2);
document.write( k);

// This code is contributed by noob2000.
</script>

Output:

15

Time Complexity: O(N) 
Space Complexity: O(1)