002. add two numbers

# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None
class (object):
    def addTwoNumbers(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        dummyHead = p = ListNode(0) # dummyHead为哑节点
        carry = 0
        while l1 or l2 or carry:
            if l1:
                carry += l1.val
                l1 = l1.next
            if l2:
                carry += l2.val
                l2 = l2.next
            carry, val = divmod(carry, 10)
            p.next = p = ListNode(val)
        return dummyHead.next