[leetcode:python] 2.Add Two Numbers

题目描述：

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)

Output: 7 -> 0 -> 8

题意：

给定两个非空链表，存放的是非负整数。数值可逆序存放，每个节点只存放一个数。使两表相加并返回和表。

假设两个表的开头都没有0，除非这个表只包含0

代码：

# 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
"""
head = l1
carry = 0
while l1 and l2:
l1.val += (l2.val+carry)
carry = l1.val/10
l1.val = l1.val%10
pre = l1
l1 = l1.next
l2 = l2.next

if l2:
pre.next = l2
l2.val += carry
carry = l2.val/10
l2.val = l2.val%10
pre = l2
while carry:
if pre.next:
pre = pre.next
pre.val += carry
carry = pre.val/10
pre.val = pre.val%10
else:
pre.next = ListNode(carry)
carry = 0

return head