class Solution:
    # @param {ListNode} l1
    # @param {ListNode} l2
    # @return {ListNode}
    def addTwoNumbers(self, l1, l2):
        def listiter(l):
            cur = l
            while cur:
                yield cur.val
                cur = cur.next


        ll1 = list(listiter(l1))
        ll2 = list(listiter(l2))
        if len(ll2) < len(ll1):
           ll1, ll2 = ll2, ll1

        for _ in range(len(ll2) - len(ll1)):
            ll1.append(0)

        head = ListNode(-1)
        cur = head
        carry = 0
        for x, y in zip(ll1, ll2):
            s = x + y + carry
            s, carry = s % 10, s // 10
            node = ListNode(s)
            cur.next = node
            cur = node
        if carry > 0:
            node = ListNode(carry)
            cur.next = node

        return head.next