002_Add_Two_Numbers.py

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


class Solution(object):
    def addTwoNumbers(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        last = 0
        head = prev = None
        while True:
            if l2 is None and l1 is None and last == 0:
                break
            val = last
            if l2 is not None:
                val += l2.val
                l2 = l2.next
            if l1 is not None:
                val += l1.val
                l1 = l1.next
            if val >= 10:
                val = val % 10
                last = 1
            else:
                last = 0
            current = ListNode(val)
            if prev is None:
                head = current
            else:
                prev.next = current
            prev = current
        return head