leetcode 2. Add Two Numbers python

题目

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

有两个链表作为输入，它们表示逆序的两个非负数。两个链表表示的是342和465。

计算它们的和并且用同样的方式逆序输出。如342+465 = 807。结果应表达为7 ->0 ->8

解答

# Definition for singly-linked list.
import math
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
      """
        carry = 0
        root = n = ListNode(0)
        while l1 or l2 or carry:
            v1 = v2 = 0
            if l1:
                v1 = l1.val
                l1 = l1.next
            if l2:
                v2 = l2.val
                l2 = l2.next
            carry, val = divmod(v1 + v2 + carry, 10)
            n.next = ListNode(val)
            n = n.next
        return root.next
"""
    测试单链表l1
"""
l1 = ListNode(2)
l1.next=ListNode(4)
l1.next.next=ListNode(3)
# while l1 is not None:
#     #print(l1.val)
#     l1=l1.next

"""
    测试单链表l2
"""
l2 = ListNode(5)
l2.next=ListNode(6)
l2.next.next=ListNode(4)
# while l2 is not None:
#     #print(l2.val)
#     l2=l2.next

a=Solution()
r=a.addTwoNumbers(l1,l2)
print(r.val)
print(r.next.val)
print(r.next.next.val)

输出结果

7
0
8

解释

感觉这位大神太牛逼了，代码写的简洁优雅。

在python中，预定义为常量False的布尔表达式、特殊对象None、空序列或集合（比如，空字符串、列表或元组）、值为0的数值型数据项等的

布尔结果为False，其他的则为True。

while l1 or l2 or carry 当l1 l2 不为空就继续循环

carry, val = divmod(v1 + v2 + carry, 10) 来判断是否有进位，如果有carry 就会将其带入下次循环，也就是实现了进位。