## Question

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order, and each of their nodes contains a single digit.

Add the two numbers and return the sum as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

**Example 1:**

Input:l1 = [2,4,3], l2 = [5,6,4]Output:[7,0,8]Explanation:342 + 465 = 807.

**Example 2:**

Input:l1 = [0], l2 = [0]Output:[0]

**Example 3:**

Input:l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9]Output:[8,9,9,9,0,0,0,1]

**Constraints:**

- The number of nodes in each linked list is in the range
`[1, 100]`

. `0 <= Node.val <= 9`

- It is guaranteed that the list represents a number that does not have leading zeros.

## Python Solution

# Definition for singly-linked list. # class ListNode: # def __init__(self, val=0, next=None): # self.val = val # self.next = next class Solution: def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode: c = 0 x = ListNode(-1) h = x while l1 or l2 or c: n1 = l1.val if l1 else 0 n2 = l2.val if l2 else 0 if l1:l1 = l1.next if l2:l2 = l2.next s = n1+n2+c c = s//10 x.next = ListNode(s%10) x = x.next return h.next