2. Add Two Numbers
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.
Input: l1 = [2,4,3], l2 = [5,6,4] Output: [7,0,8] Explanation: 342 + 465 = 807.
Input: l1 = , l2 =  Output: 
Input: l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9] Output: [8,9,9,9,0,0,0,1]
- The number of nodes in each linked list is in the range
0 <= Node.val <= 9
- It is guaranteed that the list represents a number that does not have leading zeros.
class Solution: def addTwoNumbers(self, l1: Optional[ListNode], l2: Optional[ListNode]) -> Optional[ListNode]: head = None # Reference of head which is null at this poin temp = None # Carry carry = 0 # Loop for the two lists while l1 is not None or l2 is not None: # At the start of each iteration, we should add carry from the last iteration sum_value = carry # Since the lengths of the lists may be unequal, we are checking if the # current node is null for one of the lists if l1 is not None: sum_value += l1.val l1 = l1.next if l2 is not None: sum_value += l2.val l2 = l2.next # At this point, we will add the total sum_value % 10 to the new node # in the resultant list node = ListNode(sum_value % 10) # Carry to be added in the next iteration carry = sum_value // 10 # If this is the first node or head if temp is None: temp = head = node # for any other node else: temp.next = node temp = temp.next # After the last iteration, we will check if there is carry left # If it's left then we will create a new node and add it if carry > 0: temp.next = ListNode(carry) return head
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