# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode:
        if l1 is None: 
            return l2
        if l2 is None: 
            return l1

        head = ListNode(-1)
        cur,c = head,0

        while(l1 is not None or l2 is not None):
            p1 = l1.val if l1 is not None else 0
            p2 = l2.val if l2 is not None else 0

            cur_val = p1 + p2 + c

            res = cur_val%10
            c = cur_val//10
            # print(cur_val, c)

            cur.next = ListNode(res)
            cur = cur.next

            if l1 is not None: l1 = l1.next
            if l2 is not None: l2 = l2.next

        if c == 1:
            cur.next = ListNode(c)
            cur = cur.next

        return head.next

        # while(head.next is not None):
        #     print(head.next.val)
        #     head = head.next