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.
Example
Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.
Answer:
# 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
"""
list_node = ListNode(None)
a = l1
b = l2
c = list_node
carr = 0
while a or b:
res = carr
flag_a = True
flag_b = True
if a:
res += a.val
else:
flag_a = False
if b:
res += b.val
else:
flag_b = False
if res > 9:
carr = 1
res -= 10
c.next = ListNode(1)
else:
carr = 0
c.val = res
if flag_a and a.next or flag_b and b.next:
c.next = ListNode(None)
c = c.next
if flag_a:
a = a.next
if flag_b:
b = b.next
return list_node
思路一(放弃):
1. 将ListNode逆序算出来number后相加,再生成ListNode输出,结果1562个test cases中最后第二个报错了,查看应该是数字位数太大导致计算失败,因为Python 3以后,sys.maxsize
为9223372036854775807。
思路二(代码见上):
1. 在原来的ListNode中直接计算,注意大于10的时候要进位(carr
),还有注意NoneType没有next的报错,为了应对输入的2个ListNode深度不一致,增加了flag_a
和flag_b
。
Todo:
1. 代码不够优雅;
2. 健壮性不足。