# Add two numbers represented by linked lists | Set 2

Given two numbers represented by two linked lists, the task is to write a function that returns the sum of the two linked lists in the form of a list.

Note: It is not allowed to modify the lists. Also, not allowed to use explicit extra space (Hint: Use Recursion).

Example :

Input: First List: 5->6->3, Second List: 8->4->2
Output: Resultant list: 1->4->0->5
Explanation: Sum of 563 and 842 is 1405

We have discussed a solution here which is for linked lists where the least significant digit is the first node of lists and the most significant digit is the last node. In this problem, the most significant digit is the first node and the least significant digit is the last node and we are not allowed to modify the lists. Recursion is used here to calculate the sum from right to left.

Step-by-step approach:

• Calculate sizes of given two linked lists.
• If sizes are same, then calculate sum using recursion. Hold all nodes in recursion call stack till the rightmost node, calculate the sum of rightmost nodes and forward carry to the left side.
• If size is not same, then follow below steps:
• Calculate difference of sizes of two linked lists. Let the difference be diff
• Move diff nodes ahead in the bigger linked list. Now use step 2 to calculate the sum of the smaller list and right sub-list (of the same size) of a larger list. Also, store the carry of this sum.
• Calculate the sum of the carry (calculated in the previous step) with the remaining left sub-list of a larger list. Nodes of this sum are added at the beginning of the sum list obtained the previous step.

Below is a dry run of the above approach:

Below is the implementation of the above approach.

## C++

 `// A C++ recursive program to add two linked lists` `#include ` `using` `namespace` `std;`   `// A linked List Node` `class` `Node {` `public``:` `    ``int` `data;` `    ``Node* next;` `};`   `typedef` `Node node;`   `/* A utility function to insert` `a node at the beginning of linked list */` `void` `push(Node** head_ref, ``int` `new_data)` `{` `    ``/* allocate node */` `    ``Node* new_node = ``new` `Node[(``sizeof``(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;` `}`   `/* A utility function to print linked list */` `void` `printList(Node* node)` `{` `    ``while` `(node != NULL) {` `        ``cout << node->data << ``" "``;` `        ``node = node->next;` `    ``}` `    ``cout << endl;` `}`   `// A utility function to swap two pointers` `void` `swapPointer(Node** a, Node** b)` `{` `    ``node* t = *a;` `    ``*a = *b;` `    ``*b = t;` `}`   `/* A utility function to get size of linked list */` `int` `getSize(Node* node)` `{` `    ``int` `size = 0;` `    ``while` `(node != NULL) {` `        ``node = node->next;` `        ``size++;` `    ``}` `    ``return` `size;` `}`   `// Adds two linked lists of same size` `// represented by head1 and head2 and returns` `// head of the resultant linked list. Carry` `// is propagated while returning from the recursion` `node* addSameSize(Node* head1, Node* head2, ``int``* carry)` `{` `    ``// Since the function assumes linked lists are of same` `    ``// size, check any of the two head pointers` `    ``if` `(head1 == NULL)` `        ``return` `NULL;`   `    ``int` `sum;`   `    ``// Allocate memory for sum node of current two nodes` `    ``Node* result = ``new` `Node[(``sizeof``(Node))];`   `    ``// Recursively add remaining nodes and get the carry` `    ``result->next` `        ``= addSameSize(head1->next, head2->next, carry);`   `    ``// add digits of current nodes and propagated carry` `    ``sum = head1->data + head2->data + *carry;` `    ``*carry = sum / 10;` `    ``sum = sum % 10;`   `    ``// Assign the sum to current node of resultant list` `    ``result->data = sum;`   `    ``return` `result;` `}`   `// This function is called after the` `// smaller list is added to the bigger` `// lists's sublist of same size. Once the` `// right sublist is added, the carry` `// must be added toe left side of larger` `// list to get the final result.` `void` `addCarryToRemaining(Node* head1, Node* cur, ``int``* carry,` `                         ``Node** result)` `{` `    ``int` `sum;`   `    ``// If diff. number of nodes are not traversed, add carry` `    ``if` `(head1 != cur) {` `        ``addCarryToRemaining(head1->next, cur, carry,` `                            ``result);`   `        ``sum = head1->data + *carry;` `        ``*carry = sum / 10;` `        ``sum %= 10;`   `        ``// add this node to the front of the result` `        ``push(result, sum);` `    ``}` `}`   `// The main function that adds two linked lists` `// represented by head1 and head2. The sum of` `// two lists is stored in a list referred by result` `void` `addList(Node* head1, Node* head2, Node** result)` `{` `    ``Node* cur;`   `    ``// first list is empty` `    ``if` `(head1 == NULL) {` `        ``*result = head2;` `        ``return``;` `    ``}`   `    ``// second list is empty` `    ``else` `if` `(head2 == NULL) {` `        ``*result = head1;` `        ``return``;` `    ``}`   `    ``int` `size1 = getSize(head1);` `    ``int` `size2 = getSize(head2);`   `    ``int` `carry = 0;`   `    ``// Add same size lists` `    ``if` `(size1 == size2)` `        ``*result = addSameSize(head1, head2, &carry);`   `    ``else` `{` `        ``int` `diff = ``abs``(size1 - size2);`   `        ``// First list should always be larger than second` `        ``// list. If not, swap pointers` `        ``if` `(size1 < size2)` `            ``swapPointer(&head1, &head2);`   `        ``// move diff. number of nodes in first list` `        ``for` `(cur = head1; diff--; cur = cur->next)` `            ``;`   `        ``// get addition of same size lists` `        ``*result = addSameSize(cur, head2, &carry);`   `        ``// get addition of remaining first list and carry` `        ``addCarryToRemaining(head1, cur, &carry, result);` `    ``}`   `    ``// if some carry is still there, add a new node to the` `    ``// front of the result list. e.g. 999 and 87` `    ``if` `(carry)` `        ``push(result, carry);` `}`   `// Driver code` `int` `main()` `{` `    ``Node *head1 = NULL, *head2 = NULL, *result = NULL;`   `    ``int` `arr1[] = { 9, 9, 9 };` `    ``int` `arr2[] = { 1, 8 };`   `    ``int` `size1 = ``sizeof``(arr1) / ``sizeof``(arr1[0]);` `    ``int` `size2 = ``sizeof``(arr2) / ``sizeof``(arr2[0]);`   `    ``// Create first list as 9->9->9` `    ``int` `i;` `    ``for` `(i = size1 - 1; i >= 0; --i)` `        ``push(&head1, arr1[i]);`   `    ``// Create second list as 1->8` `    ``for` `(i = size2 - 1; i >= 0; --i)` `        ``push(&head2, arr2[i]);`   `    ``addList(head1, head2, &result);`   `    ``printList(result);`   `    ``return` `0;` `}`   `// This code is contributed by rathbhupendra`

## C

 `// A C recursive program to add two linked lists`   `#include ` `#include `   `// A linked List Node` `struct` `Node {` `    ``int` `data;` `    ``struct` `Node* next;` `};`   `typedef` `struct` `Node node;`   `/* A utility function to insert a` `node at the beginning of the linked list */` `void` `push(node** head_ref, ``int` `new_data)` `{` `    ``/* allocate node */` `    ``node* new_node = (node*)``malloc``(``sizeof``(node));`   `    ``/* put in the data */` `    ``new_node->data = new_data;`   `    ``/* link the old list to the new node */` `    ``new_node->next = (*head_ref);`   `    ``/* move the head to point to the new node */` `    ``(*head_ref) = new_node;` `}`   `/* A utility function to print a linked list */` `void` `printList(node* node)` `{` `    ``while` `(node != NULL) {` `        ``printf``(``"%d "``, node->data);` `        ``node = node->next;` `    ``}` `    ``printf``(``"\n"``);` `}`   `// A utility function to swap two pointers` `void` `swapPointer(node** a, node** b)` `{` `    ``node* t = *a;` `    ``*a = *b;` `    ``*b = t;` `}`   `/* A utility function to get the size` `of a linked list */` `int` `getSize(node* node)` `{` `    ``int` `size = 0;` `    ``while` `(node != NULL) {` `        ``node = node->next;` `        ``size++;` `    ``}` `    ``return` `size;` `}`   `// Adds two linked lists of the same` `// size represented by head1` `// and head2 and returns the head of` `// the resultant linked list.` `// Carry is propagated while` `// returning from the recursion` `node* addSameSize(node* head1, node* head2, ``int``* carry)` `{` `    ``// Since the function assumes` `    ``// linked lists are of the same` `    ``// size, check any of the two` `    ``// head pointers` `    ``if` `(head1 == NULL)` `        ``return` `NULL;`   `    ``int` `sum;`   `    ``// Allocate memory for the sum` `    ``// node of the current two nodes` `    ``node* result = (node*)``malloc``(``sizeof``(node));`   `    ``// Recursively add the remaining nodes` `    ``// and get the carry` `    ``result->next` `        ``= addSameSize(head1->next, head2->next, carry);`   `    ``// add digits of the current nodes` `    ``// and propagated carry` `    ``sum = head1->data + head2->data + *carry;` `    ``*carry = sum / 10;` `    ``sum = sum % 10;`   `    ``// Assign the sum to the current` `    ``// node of the resultant list` `    ``result->data = sum;`   `    ``return` `result;` `}`   `// This function is called after` `// the smaller list is added` `// to the bigger list's sublist` `// of the same size. Once the` `// right sublist is added, the` `// carry must be added to the left` `// side of the larger list to get` `// the final result.` `void` `addCarryToRemaining(node* head1, node* cur, ``int``* carry,` `                         ``node** result)` `{` `    ``int` `sum;`   `    ``// If a different number of nodes are` `    ``// not traversed, add carry` `    ``if` `(head1 != cur) {` `        ``addCarryToRemaining(head1->next, cur, carry,` `                            ``result);`   `        ``sum = head1->data + *carry;` `        ``*carry = sum / 10;` `        ``sum %= 10;`   `        ``// add this node to the front of the result` `        ``push(result, sum);` `    ``}` `}`   `// The main function that adds two` `// linked lists represented` `// by head1 and head2. The sum of` `// two lists is stored in a` `// list referred to by result` `void` `addList(node* head1, node* head2, node** result)` `{` `    ``node* cur;`   `    ``// first list is empty` `    ``if` `(head1 == NULL) {` `        ``*result = head2;` `        ``return``;` `    ``}` `    ``// second list is empty` `    ``else` `if` `(head2 == NULL) {` `        ``*result = head1;` `        ``return``;` `    ``}`   `    ``int` `size1 = getSize(head1);` `    ``int` `size2 = getSize(head2);`   `    ``int` `carry = 0;`   `    ``// Add lists of the same size` `    ``if` `(size1 == size2)` `        ``*result = addSameSize(head1, head2, &carry);`   `    ``else` `{` `        ``int` `diff = ``abs``(size1 - size2);`   `        ``// First list should always be` `        ``// larger than the second list.` `        ``// If not, swap pointers` `        ``if` `(size1 < size2)` `            ``swapPointer(&head1, &head2);`   `        ``// move the diff. number of nodes in the first list` `        ``for` `(cur = head1; diff--; cur = cur->next)` `            ``;`   `        ``// get the addition of the same size lists` `        ``*result = addSameSize(cur, head2, &carry);`   `        ``// get the addition of the remaining first list and` `        ``// carry` `        ``addCarryToRemaining(head1, cur, &carry, result);` `    ``}`   `    ``// if some carry is still there, add a new node to the` `    ``// front of the result list. e.g. 999 and 87` `    ``if` `(carry)` `        ``push(result, carry);` `}`   `// Driver code` `int` `main()` `{` `    ``node* head1 = NULL;` `    ``node* head2 = NULL;` `    ``node* result = NULL;`   `    ``int` `arr1[] = { 9, 9, 9 };` `    ``int` `arr2[] = { 1, 8 };`   `    ``int` `size1 = ``sizeof``(arr1) / ``sizeof``(arr1[0]);` `    ``int` `size2 = ``sizeof``(arr2) / ``sizeof``(arr2[0]);`   `    ``// Create the first list as 9->9->9` `    ``int` `i;` `    ``for` `(i = size1 - 1; i >= 0; --i)` `        ``push(&head1, arr1[i]);`   `    ``// Create the second list as 1->8` `    ``for` `(i = size2 - 1; i >= 0; --i)` `        ``push(&head2, arr2[i]);`   `    ``addList(head1, head2, &result);`   `    ``printf``(``"Resultant List: "``);` `    ``printList(result);`   `    ``return` `0;` `}`

## Java

 `// A Java recursive program to add two linked lists`   `public` `class` `linkedlistATN ` `{` `    ``class` `node ` `    ``{` `        ``int` `val;` `        ``node next;`   `        ``public` `node(``int` `val) ` `        ``{` `            ``this``.val = val;` `        ``}` `    ``}` `    `  `    ``// Function to print linked list` `    ``void` `printlist(node head) ` `    ``{` `        ``while` `(head != ``null``) ` `        ``{` `            ``System.out.print(head.val + ``" "``);` `            ``head = head.next;` `        ``}` `    ``}`   `    ``node head1, head2, result;` `    ``int` `carry;`   `    ``/* A utility function to push a value to linked list */` `    ``void` `push(``int` `val, ``int` `list) ` `    ``{` `        ``node newnode = ``new` `node(val);` `        ``if` `(list == ``1``) ` `        ``{` `            ``newnode.next = head1;` `            ``head1 = newnode;` `        ``} ` `        ``else` `if` `(list == ``2``) ` `        ``{` `            ``newnode.next = head2;` `            ``head2 = newnode;` `        ``} ` `        ``else` `        ``{` `            ``newnode.next = result;` `            ``result = newnode;` `        ``}`   `    ``}`   `    ``// Adds two linked lists of same size represented by` `    ``// head1 and head2 and returns head of the resultant ` `    ``// linked list. Carry is propagated while returning ` `    ``// from the recursion` `    ``void` `addsamesize(node n, node m) ` `    ``{` `        ``// Since the function assumes linked lists are of ` `        ``// same size, check any of the two head pointers` `        ``if` `(n == ``null``)` `            ``return``;`   `        ``// Recursively add remaining nodes and get the carry` `        ``addsamesize(n.next, m.next);`   `        ``// add digits of current nodes and propagated carry` `        ``int` `sum = n.val + m.val + carry;` `        ``carry = sum / ``10``;` `        ``sum = sum % ``10``;`   `        ``// Push this to result list` `        ``push(sum, ``3``);`   `    ``}`   `    ``node cur;`   `    ``// This function is called after the smaller list is ` `    ``// added to the bigger lists's sublist of same size. ` `    ``// Once the right sublist is added, the carry must be ` `    ``// added to the left side of larger list to get the ` `    ``// final result.` `    ``void` `propogatecarry(node head1) ` `    ``{` `        ``// If diff. number of nodes are not traversed, add carry` `        ``if` `(head1 != cur) ` `        ``{` `            ``propogatecarry(head1.next);` `            ``int` `sum = carry + head1.val;` `            ``carry = sum / ``10``;` `            ``sum %= ``10``;`   `            ``// add this node to the front of the result` `            ``push(sum, ``3``);` `        ``}` `    ``}`   `    ``int` `getsize(node head) ` `    ``{` `        ``int` `count = ``0``;` `        ``while` `(head != ``null``) ` `        ``{` `            ``count++;` `            ``head = head.next;` `        ``}` `        ``return` `count;` `    ``}`   `    ``// The main function that adds two linked lists ` `    ``// represented by head1 and head2. The sum of two ` `    ``// lists is stored in a list referred by result` `    ``void` `addlists() ` `    ``{` `        ``// first list is empty` `        ``if` `(head1 == ``null``) ` `        ``{` `            ``result = head2;` `            ``return``;` `        ``}`   `        ``// first list is empty` `        ``if` `(head2 == ``null``) ` `        ``{` `            ``result = head1;` `            ``return``;` `        ``}`   `        ``int` `size1 = getsize(head1);` `        ``int` `size2 = getsize(head2);`   `        ``// Add same size lists` `        ``if` `(size1 == size2) ` `        ``{` `            ``addsamesize(head1, head2);` `        ``} ` `        ``else` `        ``{` `            ``// First list should always be larger than second list.` `            ``// If not, swap pointers` `            ``if` `(size1 < size2) ` `            ``{` `                ``node temp = head1;` `                ``head1 = head2;` `                ``head2 = temp;` `            ``}` `            ``int` `diff = Math.abs(size1 - size2);`   `            ``// move diff. number of nodes in first list` `            ``node temp = head1;` `            ``while` `(diff-- >= ``0``) ` `            ``{` `                ``cur = temp;` `                ``temp = temp.next;` `            ``}`   `            ``// get addition of same size lists` `            ``addsamesize(cur, head2);`   `            ``// get addition of remaining first list and carry` `            ``propogatecarry(head1);` `        ``}` `            ``// if some carry is still there, add a new node to ` `            ``// the front of the result list. e.g. 999 and 87` `            ``if` `(carry > ``0``)` `                ``push(carry, ``3``);` `        `  `    ``}`   `    ``// Driver program to test above functions` `    ``public` `static` `void` `main(String args[])` `    ``{` `        ``linkedlistATN list = ``new` `linkedlistATN();` `        ``list.head1 = ``null``;` `        ``list.head2 = ``null``;` `        ``list.result = ``null``;` `        ``list.carry = ``0``;` `        ``int` `arr1[] = { ``9``, ``9``, ``9` `};` `        ``int` `arr2[] = { ``1``, ``8` `};`   `        ``// Create first list as 9->9->9` `        ``for` `(``int` `i = arr1.length - ``1``; i >= ``0``; --i)` `            ``list.push(arr1[i], ``1``);`   `        ``// Create second list as 1->8` `        ``for` `(``int` `i = arr2.length - ``1``; i >= ``0``; --i)` `            ``list.push(arr2[i], ``2``);`   `        ``list.addlists();`   `        ``list.printlist(list.result);` `    ``}` `}`   `// This code is contributed by Rishabh Mahrsee`

## Python3

 `# A Python3 recursive program to add two linked lists` `class` `node:` `    ``def` `__init__(``self``, val):` `        ``self``.val ``=` `val` `        ``self``.``next` `=` `None`   `head1, head2, result ``=` `None``, ``None``, ``None` `carry ``=` `0`   `# Function to print linked list` `def` `printlist(head):` `    ``while` `head !``=` `None``:` `        ``print``(head.val, end``=``" "``)` `        ``head ``=` `head.``next`   `#  A utility function to push a value to linked list` `def` `push(val, lst):` `    ``global` `head1, head2, result` `    ``newnode ``=` `node(val)` `    ``if` `lst ``=``=` `1``:` `        ``newnode.``next` `=` `head1` `        ``head1 ``=` `newnode` `    ``elif` `lst ``=``=` `2``:` `        ``newnode.``next` `=` `head2` `        ``head2 ``=` `newnode` `    ``else``:` `        ``newnode.``next` `=` `result` `        ``result ``=` `newnode`   `# Adds two linked lists of same size represented by` `# head1 and head2 and returns head of the resultant` `# linked list. Carry is propagated while returning` `# from the recursion` `def` `addsamesize(n, m):` `    ``global` `carry` `    `  `    ``# Since the function assumes linked lists are of` `    ``# same size, check any of the two head pointers` `    ``if` `n ``=``=` `None``:` `        ``return` `      `  `    ``# Recursively add remaining nodes and get the carry` `    ``addsamesize(n.``next``, m.``next``)` `    `  `    ``# add digits of current nodes and propagated carry` `    ``sum` `=` `n.val ``+` `m.val ``+` `carry` `    ``carry ``=` `int``(``sum` `/` `10``)` `    ``sum` `=` `sum` `%` `10` `    `  `    ``# Push this to result list` `    ``push(``sum``, ``3``)`   `cur ``=` `None`   `# This function is called after the smaller list is` `# added to the bigger lists's sublist of same size.` `# Once the right sublist is added, the carry must be` `# added to the left side of larger list to get the` `# final result.` `def` `propogatecarry(head1):` `    ``global` `carry, cur` `    `  `    ``# If diff. number of nodes are not traversed, add carry` `    ``if` `head1 !``=` `cur:` `        ``propogatecarry(head1.``next``)` `        ``sum` `=` `carry ``+` `head1.val` `        ``carry ``=` `int``(``sum` `/` `10``)` `        ``sum` `%``=` `10` `        `  `        ``# add this node to the front of the result` `        ``push(``sum``, ``3``)`   `def` `getsize(head):` `    ``count ``=` `0` `    ``while` `head !``=` `None``:` `        ``count ``+``=` `1` `        ``head ``=` `head.``next` `    ``return` `count` `  `  `# The main function that adds two linked lists` `# represented by head1 and head2. The sum of two` `# lists is stored in a list referred by result` `def` `addlists():` `    ``global` `head1, head2, result, carry, cur` `    `  `    ``# first list is empty` `    ``if` `head1 ``=``=` `None``:` `        ``result ``=` `head2` `        ``return` `      `  `    ``# first list is empty` `    ``if` `head2 ``=``=` `None``:` `        ``result ``=` `head1` `        ``return` `    ``size1 ``=` `getsize(head1)` `    ``size2 ``=` `getsize(head2)` `    `  `    ``# Add same size lists` `    ``if` `size1 ``=``=` `size2:` `        ``addsamesize(head1, head2)` `    ``else``:` `      `  `        ``# First list should always be larger than second list.` `        ``# If not, swap pointers` `        ``if` `size1 < size2:` `            ``temp ``=` `head1` `            ``head1 ``=` `head2` `            ``head2 ``=` `temp` `        ``diff ``=` `abs``(size1 ``-` `size2)` `        `  `        ``# move diff. number of nodes in first list` `        ``temp ``=` `head1` `        ``while` `diff >``=` `0``:` `            ``cur ``=` `temp` `            ``temp ``=` `temp.``next` `            ``diff ``-``=` `1` `            `  `        ``# get addition of same size lists` `        ``addsamesize(cur, head2)` `        `  `        ``# get addition of remaining first list and carry` `        ``propogatecarry(head1)` `        `  `    ``# if some carry is still there, add a new node to` `    ``# the front of the result list. e.g. 999 and 87` `    ``if` `carry > ``0``:` `        ``push(carry, ``3``)`   `# Driver program to test above functions` `head1, head2, result ``=` `None``, ``None``, ``None` `carry ``=` `0` `arr1 ``=` `[``9``, ``9``, ``9``]` `arr2 ``=` `[``1``, ``8``]`   `# Create first list as 9->9->9` `for` `i ``in` `range``(``len``(arr1)``-``1``, ``-``1``, ``-``1``):` `    ``push(arr1[i], ``1``)`   `# Create second list as 1->8` `for` `i ``in` `range``(``len``(arr2)``-``1``, ``-``1``, ``-``1``):` `    ``push(arr2[i], ``2``)`   `addlists()` `printlist(result)`   `# This code is contributed by Prajwal Kandekar`

## C#

 `// A C# recursive program to add two linked lists` `using` `System;` ` `  `public` `class` `linkedlistATN{` `    `  `class` `node ` `{` `    ``public` `int` `val;` `    ``public` `node next;`   `    ``public` `node(``int` `val) ` `    ``{` `        ``this``.val = val;` `    ``}` `}` ` `  `// Function to print linked list` `void` `printlist(node head) ` `{` `    ``while` `(head != ``null``) ` `    ``{` `        ``Console.Write(head.val + ``" "``);` `        ``head = head.next;` `    ``}` `}`   `node head1, head2, result;` `int` `carry;`   `// A utility function to push a ` `// value to linked list ` `void` `push(``int` `val, ``int` `list) ` `{` `    ``node newnode = ``new` `node(val);` `    `  `    ``if` `(list == 1) ` `    ``{` `        ``newnode.next = head1;` `        ``head1 = newnode;` `    ``} ` `    ``else` `if` `(list == 2) ` `    ``{` `        ``newnode.next = head2;` `        ``head2 = newnode;` `    ``} ` `    ``else` `    ``{` `        ``newnode.next = result;` `        ``result = newnode;` `    ``}`   `}`   `// Adds two linked lists of same size represented by` `// head1 and head2 and returns head of the resultant ` `// linked list. Carry is propagated while returning ` `// from the recursion` `void` `addsamesize(node n, node m) ` `{` `    `  `    ``// Since the function assumes linked` `    ``// lists are of same size, check any` `    ``// of the two head pointers` `    ``if` `(n == ``null``)` `        ``return``;`   `    ``// Recursively add remaining nodes` `    ``// and get the carry` `    ``addsamesize(n.next, m.next);`   `    ``// Add digits of current nodes ` `    ``// and propagated carry` `    ``int` `sum = n.val + m.val + carry;` `    ``carry = sum / 10;` `    ``sum = sum % 10;`   `    ``// Push this to result list` `    ``push(sum, 3);` `}`   `node cur;`   `// This function is called after the smaller ` `// list is added to the bigger lists's sublist ` `// of same size. Once the right sublist is added,` `// the carry must be added to the left side of ` `// larger list to get the final result.` `void` `propogatecarry(node head1) ` `{` `    `  `    ``// If diff. number of nodes are ` `    ``// not traversed, add carry` `    ``if` `(head1 != cur) ` `    ``{` `        ``propogatecarry(head1.next);` `        ``int` `sum = carry + head1.val;` `        ``carry = sum / 10;` `        ``sum %= 10;`   `        ``// Add this node to the front ` `        ``// of the result` `        ``push(sum, 3);` `    ``}` `}`   `int` `getsize(node head) ` `{` `    ``int` `count = 0;` `    ``while` `(head != ``null``) ` `    ``{` `        ``count++;` `        ``head = head.next;` `    ``}` `    ``return` `count;` `}`   `// The main function that adds two linked ` `// lists represented by head1 and head2. ` `// The sum of two lists is stored in a ` `// list referred by result` `void` `addlists() ` `{` `    `  `    ``// First list is empty` `    ``if` `(head1 == ``null``) ` `    ``{` `        ``result = head2;` `        ``return``;` `    ``}`   `    ``// Second list is empty` `    ``if` `(head2 == ``null``) ` `    ``{` `        ``result = head1;` `        ``return``;` `    ``}`   `    ``int` `size1 = getsize(head1);` `    ``int` `size2 = getsize(head2);`   `    ``// Add same size lists` `    ``if` `(size1 == size2) ` `    ``{` `        ``addsamesize(head1, head2);` `    ``} ` `    ``else` `    ``{` `        `  `        ``// First list should always be` `        ``// larger than second list.` `        ``// If not, swap pointers` `        ``if` `(size1 < size2) ` `        ``{` `            ``node temp = head1;` `            ``head1 = head2;` `            ``head2 = temp;` `        ``}` `        `  `        ``int` `diff = Math.Abs(size1 - size2);`   `        ``// Move diff. number of nodes in` `        ``// first list` `        ``node tmp = head1;` `        `  `        ``while` `(diff-- >= 0) ` `        ``{` `            ``cur = tmp;` `            ``tmp = tmp.next;` `        ``}`   `        ``// Get addition of same size lists` `        ``addsamesize(cur, head2);`   `        ``// Get addition of remaining ` `        ``// first list and carry` `        ``propogatecarry(head1);` `    ``}` `        ``// If some carry is still there, ` `        ``// add a new node to the front of` `        ``// the result list. e.g. 999 and 87` `        ``if` `(carry > 0)` `            ``push(carry, 3);` `}`   `// Driver code` `public` `static` `void` `Main(``string` `[]args)` `{` `    ``linkedlistATN list = ``new` `linkedlistATN();` `    ``list.head1 = ``null``;` `    ``list.head2 = ``null``;` `    ``list.result = ``null``;` `    ``list.carry = 0;` `    `  `    ``int` `[]arr1 = { 9, 9, 9 };` `    ``int` `[]arr2 = { 1, 8 };`   `    ``// Create first list as 9->9->9` `    ``for``(``int` `i = arr1.Length - 1; i >= 0; --i)` `        ``list.push(arr1[i], 1);`   `    ``// Create second list as 1->8` `    ``for``(``int` `i = arr2.Length - 1; i >= 0; --i)` `        ``list.push(arr2[i], 2);`   `    ``list.addlists();`   `    ``list.printlist(list.result);` `}` `}`   `// This code is contributed by rutvik_56`

## Javascript

 ``

Output

```1 0 1 7

```

Time Complexity: O(m+n) where m and n are the sizes of given two linked lists.
Auxiliary Space: O(m+n) for call stack

Iterative Approach:

This implementation does not have any recursion call overhead, which means it is an iterative solution.

Since we need to start adding numbers from the last of the two linked lists. So, here we will use the stack data structure to implement this.

• We will firstly make two stacks from the given two linked lists.
• Then, we will run a loop till both stack become empty.
• in every iteration, we keep the track of the carry.
• In the end, if carry>0, that means we need extra node at the start of the resultant list to accommodate this carry.

Below is the implementation of the above approach.

## C++

 `// C++ Iterative program to add two linked lists  ` `#include ` `using` `namespace` `std; ` `  `  `// A linked List Node  ` `class` `Node  ` `{  ` `    ``public``: ` `    ``int` `data;  ` `    ``Node* next;  ` `};`   `// to push a new node to linked list` `void` `push(Node** head_ref, ``int` `new_data)  ` `{  ` `    ``/* allocate node */` `    ``Node* new_node = ``new` `Node[(``sizeof``(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;  ` `}`   `// to add two new numbers` `Node* addTwoNumList(Node* l1, Node* l2) {` `    ``stack<``int``> s1,s2;` `    ``while``(l1!=NULL){` `        ``s1.push(l1->data);` `        ``l1=l1->next;` `    ``}` `    ``while``(l2!=NULL){` `        ``s2.push(l2->data);` `        ``l2=l2->next;` `    ``}` `    ``int` `carry=0;` `    ``Node* result=NULL;` `    ``while``(s1.empty()==``false` `|| s2.empty()==``false``){` `        ``int` `a=0,b=0;` `        ``if``(s1.empty()==``false``){` `            ``a=s1.top();s1.pop();` `        ``}` `        ``if``(s2.empty()==``false``){` `            ``b=s2.top();s2.pop();` `        ``}` `        ``int` `total=a+b+carry;` `        ``Node* temp=``new` `Node();` `        ``temp->data=total%10;` `        ``carry=total/10;` `        ``if``(result==NULL){` `            ``result=temp;` `        ``}``else``{` `            ``temp->next=result;` `            ``result=temp;` `        ``}` `    ``}` `    ``if``(carry!=0){` `        ``Node* temp=``new` `Node();` `        ``temp->data=carry;` `        ``temp->next=result;` `        ``result=temp;` `    ``}` `    ``return` `result;` `}`   `// to print a linked list` `void` `printList(Node *node)  ` `{  ` `    ``while` `(node != NULL)  ` `    ``{  ` `        ``cout<data<<``" "``;  ` `        ``node = node->next;  ` `    ``}  ` `    ``cout<6->7  ` `    ``int` `i;  ` `    ``for` `(i = size1-1; i >= 0; --i)  ` `        ``push(&head1, arr1[i]);  ` `  `  `    ``// Create second list as 1->8  ` `    ``for` `(i = size2-1; i >= 0; --i)  ` `        ``push(&head2, arr2[i]);  ` `    `  `    ``Node* result=addTwoNumList(head1, head2);` `    ``printList(result);  ` `  `  `    ``return` `0;  ` `}`

## Java

 `// Java Iterative program to add ` `// two linked lists  ` `import` `java.io.*;` `import` `java.util.*;`   `class` `GFG{` `    `  `static` `class` `Node` `{` `    ``int` `data;` `    ``Node next;` `    `  `    ``public` `Node(``int` `data)` `    ``{ ` `        ``this``.data = data;` `    ``}` `}`   `static` `Node l1, l2, result;`   `// To push a new node to linked list` `public` `static` `void` `push(``int` `new_data)` `{` `    `  `    ``// Allocate node ` `    ``Node new_node = ``new` `Node(``0``);`   `    ``// Put in the data ` `    ``new_node.data = new_data;`   `    ``// Link the old list of the new node ` `    ``new_node.next = l1;`   `    ``// Move the head to point to the new node ` `    ``l1 = new_node;` `}`   `public` `static` `void` `push1(``int` `new_data)` `{` `    `  `    ``// Allocate node ` `    ``Node new_node = ``new` `Node(``0``);`   `    ``// Put in the data ` `    ``new_node.data = new_data;`   `    ``// Link the old list of the new node ` `    ``new_node.next = l2;`   `    ``// Move the head to point to` `    ``// the new node ` `    ``l2 = new_node;` `}`   `// To add two new numbers` `public` `static` `Node addTwoNumbers()` `{` `    ``Stack stack1 = ``new` `Stack<>();` `    ``Stack stack2 = ``new` `Stack<>();`   `    ``while` `(l1 != ``null``)` `    ``{` `        ``stack1.add(l1.data);` `        ``l1 = l1.next;` `    ``}`   `    ``while` `(l2 != ``null``) ` `    ``{` `        ``stack2.add(l2.data);` `        ``l2 = l2.next;` `    ``}`   `    ``int` `carry = ``0``;` `    ``Node result = ``null``;`   `    ``while` `(!stack1.isEmpty() ||` `           ``!stack2.isEmpty()) ` `    ``{` `        ``int` `a = ``0``, b = ``0``;`   `        ``if` `(!stack1.isEmpty()) ` `        ``{` `            ``a = stack1.pop();` `        ``}`   `        ``if` `(!stack2.isEmpty()) ` `        ``{` `            ``b = stack2.pop();` `        ``}`   `        ``int` `total = a + b + carry;`   `        ``Node temp = ``new` `Node(total % ``10``);` `        ``carry = total / ``10``;`   `        ``if` `(result == ``null``) ` `        ``{` `            ``result = temp;` `        ``}` `        ``else` `        ``{` `            ``temp.next = result;` `            ``result = temp;` `        ``}` `    ``}`   `    ``if` `(carry != ``0``)` `    ``{` `        ``Node temp = ``new` `Node(carry);` `        ``temp.next = result;` `        ``result = temp;` `    ``}` `    ``return` `result;` `}`   `// To print a linked list` `public` `static` `void` `printList()` `{` `    ``while` `(result != ``null``) ` `    ``{` `        ``System.out.print(result.data + ``" "``);` `        ``result = result.next;` `    ``}` `    ``System.out.println();` `}`   `// Driver code` `public` `static` `void` `main(String[] args)` `{` `    ``int` `arr1[] = { ``5``, ``6``, ``7` `};` `    ``int` `arr2[] = { ``1``, ``8` `};`   `    ``int` `size1 = ``3``;` `    ``int` `size2 = ``2``;`   `    ``// Create first list as 5->6->7` `    ``int` `i;` `    ``for``(i = size1 - ``1``; i >= ``0``; --i)` `        ``push(arr1[i]);`   `    ``// Create second list as 1->8` `    ``for``(i = size2 - ``1``; i >= ``0``; --i)` `        ``push1(arr2[i]);`   `    ``result = addTwoNumbers();`   `    ``printList();` `}` `}`   `// This code is contributed by RohitOberoi`

## Python3

 `# Python Iterative program to add` `# two linked lists    ` `class` `Node:` `    ``def` `__init__(``self``,val):` `        ``self``.data ``=` `val` `        ``self``.``next` `=` `None` `    `  `l1, l2, result ``=` `None``,``None``,``0`   `# To push a new node to linked list` `def` `push(new_data):`   `    ``global` `l1`   `    ``# Allocate node` `    ``new_node ``=` `Node(``0``)`   `    ``# Put in the data` `    ``new_node.data ``=` `new_data`   `    ``# Link the old list of the new node` `    ``new_node.``next` `=` `l1`   `    ``# Move the head to point to the new node` `    ``l1 ``=` `new_node`     `def` `push1(new_data):`   `    ``global` `l2`   `    ``# Allocate node` `    ``new_node ``=` `Node(``0``)`   `    ``# Put in the data` `    ``new_node.data ``=` `new_data`   `    ``# Link the old list of the new node` `    ``new_node.``next` `=` `l2`   `    ``# Move the head to point to` `    ``# the new node` `    ``l2 ``=` `new_node`   `# To add two new numbers` `def` `addTwoNumbers():`   `    ``global` `l1,l2,result`   `    ``stack1 ``=` `[]` `    ``stack2 ``=` `[]`   `    ``while` `(l1 !``=` `None``):` `        ``stack1.append(l1.data)` `        ``l1 ``=` `l1.``next`   `    ``while` `(l2 !``=` `None``):` `        ``stack2.append(l2.data)` `        ``l2 ``=` `l2.``next`   `    ``carry ``=` `0` `    ``result ``=` `None`   `    ``while` `(``len``(stack1) !``=` `0` `or` `len``(stack2) !``=` `0``):` `        ``a,b ``=` `0``,``0`   `        ``if` `(``len``(stack1) !``=` `0``):` `            ``a ``=` `stack1.pop()`   `        ``if` `(``len``(stack2) !``=` `0``):` `            ``b ``=` `stack2.pop()`   `        ``total ``=` `a ``+` `b ``+` `carry`   `        ``temp ``=` `Node(total ``%` `10``)` `        ``carry ``=` `total ``/``/` `10`   `        ``if` `(result ``=``=` `None``):` `            ``result ``=` `temp` `        ``else``:` `            ``temp.``next` `=` `result` `            ``result ``=` `temp`     `    ``if` `(carry !``=` `0``):` `        ``temp ``=` `Node(carry)` `        ``temp.``next` `=` `result` `        ``result ``=` `temp` `        `  `    ``return` `result`     `# To print a linked list` `def` `printList():`   `    ``global` `result`   `    ``while` `(result !``=` `None``):` `        ``print``(result.data ,end ``=` `" "``)` `        ``result ``=` `result.``next`   `# Driver code` `    `  `arr1 ``=` `[ ``5``, ``6``, ``7` `]` `arr2 ``=` `[ ``1``, ``8` `]`   `size1 ``=` `3` `size2 ``=` `2`   `# Create first list as 5->6->7`   `for` `i ``in` `range``(size1``-``1``,``-``1``,``-``1``):` `    ``push(arr1[i])`   `# Create second list as 1->8` `for` `i ``in` `range``(size2``-``1``,``-``1``,``-``1``):` `    ``push1(arr2[i])`   `result ``=` `addTwoNumbers()`   `printList()`   `# This code is contributed by shinjanpatra`

## C#

 `// C# Iterative program to add ` `// two linked lists  ` `using` `System;` `using` `System.Collections;`   `class` `GFG{`   `  ``public` `class` `Node` `  ``{` `    ``public` `int` `data;` `    ``public` `Node next;`   `    ``public` `Node(``int` `data)` `    ``{ ` `      ``this``.data = data;` `    ``}` `  ``}`   `  ``static` `Node l1, l2, result;`   `  ``// To push a new node to linked list` `  ``public` `static` `void` `push(``int` `new_data)` `  ``{`   `    ``// Allocate node ` `    ``Node new_node = ``new` `Node(0);`   `    ``// Put in the data ` `    ``new_node.data = new_data;`   `    ``// Link the old list of the new node ` `    ``new_node.next = l1;`   `    ``// Move the head to point to the new node ` `    ``l1 = new_node;` `  ``}`   `  ``public` `static` `void` `push1(``int` `new_data)` `  ``{`   `    ``// Allocate node ` `    ``Node new_node = ``new` `Node(0);`   `    ``// Put in the data ` `    ``new_node.data = new_data;`   `    ``// Link the old list of the new node ` `    ``new_node.next = l2;`   `    ``// Move the head to point to` `    ``// the new node ` `    ``l2 = new_node;` `  ``}`   `  ``// To add two new numbers` `  ``public` `static` `Node addTwoNumbers()` `  ``{` `    ``Stack stack1 = ``new` `Stack();` `    ``Stack stack2 = ``new` `Stack();`   `    ``while` `(l1 != ``null``)` `    ``{` `      ``stack1.Push(l1.data);` `      ``l1 = l1.next;` `    ``}` `    ``while` `(l2 != ``null``) ` `    ``{` `      ``stack2.Push(l2.data);` `      ``l2 = l2.next;` `    ``}`   `    ``int` `carry = 0;` `    ``Node result = ``null``;` `    ``while` `(stack1.Count != 0 ||` `           ``stack2.Count != 0) ` `    ``{` `      ``int` `a = 0, b = 0;`   `      ``if` `(stack1.Count != 0) ` `      ``{` `        ``a = (``int``)stack1.Pop();` `      ``}`   `      ``if` `(stack2.Count != 0) ` `      ``{` `        ``b = (``int``)stack2.Pop();` `      ``}`   `      ``int` `total = a + b + carry;` `      ``Node temp = ``new` `Node(total % 10);` `      ``carry = total / 10;`   `      ``if` `(result == ``null``) ` `      ``{` `        ``result = temp;` `      ``}` `      ``else` `      ``{` `        ``temp.next = result;` `        ``result = temp;` `      ``}` `    ``}`   `    ``if` `(carry != 0)` `    ``{` `      ``Node temp = ``new` `Node(carry);` `      ``temp.next = result;` `      ``result = temp;` `    ``}` `    ``return` `result;` `  ``}`   `  ``// To print a linked list` `  ``public` `static` `void` `printList()` `  ``{` `    ``while` `(result != ``null``) ` `    ``{` `      ``Console.Write(result.data + ``" "``);` `      ``result = result.next;` `    ``}` `    ``Console.WriteLine();` `  ``}`   `  ``// Driver code` `  ``public` `static` `void` `Main(``string``[] args)` `  ``{` `    ``int` `[]arr1 = { 5, 6, 7 };` `    ``int` `[]arr2 = { 1, 8 };` `    ``int` `size1 = 3;` `    ``int` `size2 = 2;`   `    ``// Create first list as 5->6->7` `    ``int` `i;` `    ``for``(i = size1 - 1; i >= 0; --i)` `      ``push(arr1[i]);`   `    ``// Create second list as 1->8` `    ``for``(i = size2 - 1; i >= 0; --i)` `      ``push1(arr2[i]);` `    ``result = addTwoNumbers();` `    ``printList();` `  ``}` `}`   `// This code is contributed by pratham76`

## Javascript

 ``

Output

```5 8 5

```

Time Complexity: O(m+n) where m and n are the sizes of given two linked lists.
Auxiliary Space: O(m+n)

### Another Approach (Simple iteration with 2 pointers)

To add two numbers in a linked list, we can simply iterate the 2 linked lists and take the sum of the values in nodes along with maintaining a carry. While taking sums add the previous carry to it and add a new node to the result containing the last digit in the sum and update the carry for the next iteration.

#### Step-by-step approach:

• Use 2 pointers to store the head of each linked list and initialize carry as 0.
• Declare a pointer to the node to store our answer.
• Iterate through both the linked list and add the digits pointed by the pointers (if we have reached the end of one of the linked lists and have no further nodes, consider its value as 0 while taking the sum).
• Add a new node with ((sum+carry)%10) as value to our answer and update carry as (sum + carry)/10.
• Repeat steps 3 and 4 till we reach the end of both the linked lists.
• After traversing both the linked lists, if carry > 0 then add this carry to our answer as a new node.

Below is the implementation of the above approach:

## C++

 `#include` `using` `namespace` `std;`   `struct` `Node {` `    ``int` `val;` `    ``Node* next;`   `    ``Node(``int` `value){` `        ``val = value;` `        ``next = NULL;` `    ``}` `};`   `void` `push_front(Node** head, ``int` `new_val){` `    ``Node* new_node = ``new` `Node(new_val);` `    ``new_node->next = *head;` `    ``*head = new_node;` `}`   `void` `printList(Node* head){` `    ``Node* i = head;` `    ``while``(i){` `        ``cout<val<<``" "``;` `        ``i = i->next;` `    ``}` `    ``cout<<``"\n"``;` `}`   `// function to add 2 numbers given as linked lists` `Node* add(Node* l1, Node* l2){` `    ``Node* ans = ``new` `Node(0);` `    ``Node* curr = ans;` `    ``int` `carry = 0;` `    ``while``(l1 || l2){` `        ``int` `sum = 0;` `        ``if``(l1) sum += l1->val;` `        ``if``(l2) sum += l2->val;` `        ``sum += carry;`   `        ``curr->next = ``new` `Node(sum%10);` `        ``curr = curr->next;`   `        ``carry = sum/10;`   `        ``if``(l1) l1 = l1->next;` `        ``if``(l2) l2 = l2->next;` `    ``}`   `    ``if``(carry){` `        ``curr->next = ``new` `Node(carry);` `    ``}` `    ``ans = ans->next;` `    ``return` `ans;` `}`   `int` `main(){` `    ``Node* l1 = NULL;`   `    ``push_front(&l1, 1);` `    ``push_front(&l1, 5);`   `    ``Node* l2 = NULL;`   `    ``push_front(&l2, 3);` `    ``push_front(&l2, 9);` `    ``push_front(&l2, 7);`   `    ``// l1-> 5 1   =  15` `    ``// l2-> 7 9 3 = 397`   `    ``Node* sum = add(l1,l2);`   `    ``printList(sum);` `    ``// 2 1 4      = 412` `}`

## Java

 `/*package whatever //do not write package name here */`   `class` `Node ` `{` `    ``int` `val;` `    ``Node next;` `    ``Node(``int` `value)` `    ``{` `        ``val = value;` `        ``next = ``null``;` `    ``}` `}` `class` `AddTwoLL ` `{` `    ``static` `void` `push_front(Node head, ``int` `new_val)` `    ``{` `        ``Node new_node = ``new` `Node(new_val);` `        ``new_node.next =head;` `        ``head = new_node;` `    ``}` `    ``static` `void` `printList(Node head)` `    ``{` `        ``Node i = head;` `        ``while``(i!=``null``)` `        ``{` `            ``System.out.print(i.val+``" "``);` `            ``i = i.next;` `        ``}` `        ``System.out.println();` `    ``}` `    ``// function to reverse a linked list` `    ``static` `Node reverse_it(Node head)` `    ``{` `        ``Node prev = ``null``;` `        ``Node curr = head, next;` `        ``while``(curr!=``null``)` `        ``{` `            ``next = curr.next;` `            ``curr.next = prev;` `            ``prev = curr;` `            ``curr = next;` `        ``}` `        ``return` `prev;` `    ``}` `    ``// function to convert a linked list to integer` `    ``static` `int` `to_integer(Node head){` `        ``int` `num = ``0``;` `        ``Node curr = head;` `        ``while``(curr!=``null``)` `        ``{` `            ``int` `digit = curr.val;` `            ``num = num*``10` `+ digit;` `            ``curr = curr.next;` `        ``}` `        ``return` `num;` `    ``}` `    ``// function to convert a number to a linked list containing digits in reverse order` `    ``static` `Node to_linkedlist(``int` `x)` `    ``{` `        ``Node head = ``new` `Node(``0``);` `        ``if``(x==``0``) ``return` `head;` `        ``Node curr = head;` `        ``while``(x>``0``)` `        ``{` `            ``int` `d = x%``10``;` `            ``x /= ``10``;` `            ``curr.next = ``new` `Node(d);` `            ``curr = curr.next;` `        ``}` `        ``return` `head.next;` `    ``}` `    ``// function to add 2 numbers given as linked lists` `    ``static` `Node add_list(Node l1, Node l2)` `    ``{` `        ``// reversing the 2 linked lists` `        ``l1 = reverse_it(l1);` `        ``l2 = reverse_it(l2);` `    `  `        ``// converting them into integers` `        ``int` `num1 = to_integer(l1);` `        ``int` `num2 = to_integer(l2);` `        `  `        ``int` `sum = num1 + num2;` `        ``// converting the sum back to` `        ``// a linked list` `        ``Node ans = to_linkedlist(sum);` `        `  `        ``return` `ans;` `    ``}` `    ``public` `static` `void` `main(String [] args)` `    ``{` `        ``Node l1 = ``null``;` `    `  `        ``push_front(l1, ``1``);` `        ``push_front(l1, ``5``);` `    `  `        ``Node l2 = ``null``;` `    `  `        ``push_front(l2, ``3``);` `        ``push_front(l2, ``9``);` `        ``push_front(l2, ``7``);` `    `  `        ``// l1-> 5 1` `        ``// l2-> 7 9 3` `    `  `        ``Node sum = add_list(l1,l2);` `    `  `        ``printList(sum);` `        ``// 2 1 4` `    ``}` `}`

## Python3

 `# Add two numbers represented by linked lists | Set 2` `class` `Node:` `    ``def` `__init__(``self``, value):` `        ``self``.val ``=` `value` `        ``self``.``next` `=` `None`     `def` `push_front(head, new_val):` `    ``new_node ``=` `Node(new_val)` `    ``new_node.``next` `=` `head` `    ``head ``=` `new_node` `    ``return` `head`     `def` `print_list(head):` `    ``i ``=` `head` `    ``while` `i:` `        ``print``(i.val, end``=``" "``)` `        ``i ``=` `i.``next` `    ``print``()`     `def` `add(l1, l2):` `    ``ans ``=` `Node(``0``)` `    ``curr ``=` `ans` `    ``carry ``=` `0`   `    ``while` `l1 ``or` `l2:` `        ``sum_val ``=` `0` `        ``if` `l1:` `            ``sum_val ``+``=` `l1.val` `            ``l1 ``=` `l1.``next` `        ``if` `l2:` `            ``sum_val ``+``=` `l2.val` `            ``l2 ``=` `l2.``next` `        ``sum_val ``+``=` `carry`   `        ``curr.``next` `=` `Node(sum_val ``%` `10``)` `        ``curr ``=` `curr.``next` `        ``carry ``=` `sum_val ``/``/` `10`   `    ``if` `carry:` `        ``curr.``next` `=` `Node(carry)`   `    ``ans ``=` `ans.``next` `    ``return` `ans`     `# Creating linked list l1: 5 -> 1` `l1 ``=` `None` `l1 ``=` `push_front(l1, ``1``)` `l1 ``=` `push_front(l1, ``5``)`   `# Creating linked list l2: 7 -> 9 -> 3` `l2 ``=` `None` `l2 ``=` `push_front(l2, ``3``)` `l2 ``=` `push_front(l2, ``9``)` `l2 ``=` `push_front(l2, ``7``)`   `# l1: 5 -> 1   =  15` `# l2: 7 -> 9 -> 3 = 397`   `# Adding two linked lists` `sum_list ``=` `add(l1, l2)`   `# Printing the resulting linked list` `print_list(sum_list)` `# Output: 2 1 4   = 412`   `# This code is contributed by uomkar369`

## C#

 `using` `System;` `class` `Node` `{` `    ``public` `int` `val;` `    ``public` `Node next;`   `    ``public` `Node(``int` `value)` `    ``{` `        ``val = value;` `        ``next = ``null``;` `    ``}` `}`   `class` `AddTwoLL` `{` `    ``static` `void` `push_front(``ref` `Node head, ``int` `new_val)` `    ``{` `        ``Node new_node = ``new` `Node(new_val);` `        ``new_node.next = head;` `        ``head = new_node;` `    ``}`   `    ``static` `void` `printList(Node head)` `    ``{` `        ``Node i = head;` `        ``while` `(i != ``null``)` `        ``{` `            ``Console.Write(i.val + ``" "``);` `            ``i = i.next;` `        ``}` `        ``Console.WriteLine();` `    ``}`   `    ``// Function to reverse a linked list` `    ``static` `Node reverse_it(Node head)` `    ``{` `        ``Node prev = ``null``;` `        ``Node curr = head;` `        ``Node next;` `        ``while` `(curr != ``null``)` `        ``{` `            ``next = curr.next;` `            ``curr.next = prev;` `            ``prev = curr;` `            ``curr = next;` `        ``}` `        ``return` `prev;` `    ``}`   `    ``// Function to convert a linked list to integer` `    ``static` `int` `to_integer(Node head)` `    ``{` `        ``int` `num = 0;` `        ``Node curr = head;` `        ``while` `(curr != ``null``)` `        ``{` `            ``int` `digit = curr.val;` `            ``num = num * 10 + digit;` `            ``curr = curr.next;` `        ``}` `        ``return` `num;` `    ``}`   `    ``// Function to convert a number to a linked list containing digits in reverse order` `    ``static` `Node to_linkedlist(``int` `x)` `    ``{` `        ``Node head = ``new` `Node(0);` `        ``if` `(x == 0) ``return` `head;` `        ``Node curr = head;` `        ``while` `(x > 0)` `        ``{` `            ``int` `d = x % 10;` `            ``x /= 10;` `            ``curr.next = ``new` `Node(d);` `            ``curr = curr.next;` `        ``}` `        ``return` `head.next;` `    ``}`   `    ``// Function to add 2 numbers given as linked lists` `    ``static` `Node add_list(Node l1, Node l2)` `    ``{` `        ``// Reversing the 2 linked lists` `        ``l1 = reverse_it(l1);` `        ``l2 = reverse_it(l2);`   `        ``// Converting them into integers` `        ``int` `num1 = to_integer(l1);` `        ``int` `num2 = to_integer(l2);`   `        ``int` `sum = num1 + num2;` `        ``// Converting the sum back to` `        ``// a linked list` `        ``Node ans = to_linkedlist(sum);`   `        ``return` `ans;` `    ``}`   `    ``public` `static` `void` `Main(``string``[] args)` `    ``{` `        ``Node l1 = ``null``;`   `        ``push_front(``ref` `l1, 1);` `        ``push_front(``ref` `l1, 5);`   `        ``Node l2 = ``null``;`   `        ``push_front(``ref` `l2, 3);` `        ``push_front(``ref` `l2, 9);` `        ``push_front(``ref` `l2, 7);`   `        ``// l1-> 5 1` `        ``// l2-> 7 9 3`   `        ``Node sum = add_list(l1, l2);`   `        ``printList(sum);` `        ``// 2 1 4` `    ``}` `}`

## Javascript

 `class Node {` `    ``constructor(value) {` `        ``this``.val = value;` `        ``this``.next = ``null``;` `    ``}` `}`   `function` `pushFront(head, newVal) {` `    ``const newNode = ``new` `Node(newVal);` `    ``newNode.next = head;` `    ``return` `newNode;` `}`   `function` `printList(head) {` `    ``let current = head;` `    ``while` `(current) {` `        ``process.stdout.write(current.val + ``" "``);` `        ``current = current.next;` `    ``}` `    ``console.log();` `}`   `// Function to add two numbers given as linked lists` `function` `add(l1, l2) {` `    ``const ans = ``new` `Node(0);` `    ``let curr = ans;` `    ``let carry = 0;`   `    ``while` `(l1 || l2) {` `        ``let sum = 0;` `        ``if` `(l1) sum += l1.val;` `        ``if` `(l2) sum += l2.val;` `        ``sum += carry;`   `        ``curr.next = ``new` `Node(sum % 10);` `        ``curr = curr.next;`   `        ``carry = Math.floor(sum / 10);`   `        ``if` `(l1) l1 = l1.next;` `        ``if` `(l2) l2 = l2.next;` `    ``}`   `    ``if` `(carry) {` `        ``curr.next = ``new` `Node(carry);` `    ``}`   `    ``return` `ans.next;` `}`   `// Main function` `function` `main() {` `    ``let l1 = ``null``;`   `    ``l1 = pushFront(l1, 1);` `    ``l1 = pushFront(l1, 5);`   `    ``let l2 = ``null``;`   `    ``l2 = pushFront(l2, 3);` `    ``l2 = pushFront(l2, 9);` `    ``l2 = pushFront(l2, 7);`   `    ``// l1-> 5 1   =  15` `    ``// l2-> 7 9 3 = 397`   `    ``const sum = add(l1, l2);`   `    ``printList(sum);` `    ``// 2 1 4      = 412` `}`   `main();`

Time Complexity: O(n).
Space Complexity: O(max(n,m)), to avoid the use of extra space we can store the sum in one of the linked lists itself.

Related Article: Add two numbers represented by linked lists | Set 1
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