# 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

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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 ` ` `  `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 off 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 `

Output:

```15
```

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

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Improved By : Rajput-Ji