2. Add Two Numbers

Medium

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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.

# 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: Optional[ListNode], l2: Optional[ListNode]) -> Optional[ListNode]:
        carry = 0
        head = new = ListNode()
        while l1 and l2:
            num1 = l1.val
            num2 = l2.val
            sumation = num1 + num2 + carry
            carry = (sumation) // 10
            new_node = ListNode(sumation % 10)
            new.next = new_node
            new = new_node
            l1 = l1.next
            l2 = l2.next
        left_node = l1 or l2
        while left_node:
            num2 = left_node.val
            sumation = num2 + carry
            carry = (sumation) // 10
            new_node = ListNode(sumation % 10)
            new.next = new_node
            new = new_node
            left_node = left_node.next
        if carry:
            new_node = ListNode(carry)
            new.next = new_node
            new = new_node
        return head.next