Leetcode 之 Add Two Numbers

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

class Solution:
    def addTwoNumbers(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        head = ListNode(0)
        ptr = head
        carry = 0
        while True:
            if l1 != None:
                carry += l1.val
                l1 = l1.next
            if l2 != None:
                carry += l2.val
                l2 = l2.next
            ptr.val = carry % 10
            carry = int(carry / 10)
            if l1 != None or l2 != None or carry != 0:
                ptr.next = ListNode(0)
                ptr = ptr.next
            else:
                break
        return head