给出两个 非空 的链表用来表示两个非负的整数。其中，它们各自的位数是按照 逆序 的方式存储的，并且它们的每个节点只能存储 一位 数字。
如果，我们将这两个数相加起来，则会返回一个新的链表来表示它们的和。
您可以假设除了数字 0 之外，这两个数都不会以 0 开头。
示例：
输入：(2 -> 4 -> 3) + (5 -> 6 -> 4)
输出：7 -> 0 -> 8
原因：342 + 465 = 807
"""
第一次：代码太啰嗦！主要思想是，设置进位标志tmp，遍历两个列表对应位置的值，将对应位置的两个值与进位值相加，result中保留个位值，tmp中保留进位值。分四种情况：l1和l2的位数相同时依次相加；l1的位数大于l2位数时，将l1多余位append到result中，l2位数大于l1位数，将l2多余位append到result中；最后将tmp值append到result中
"""
# Definition for singly-linked list.
# class ListNode(object):
# def __init__(self, x):
# self.val = x
# self.next = Noneclass Solution(object):
def addTwoNumbers(self, l1, l2):
"""
:type l1: ListNode
:type l2: ListNode
:rtype: ListNode
"""
tmp = 0
result = []
while l1 != None and l2 != None:
add = l1.val + l2.val + tmp
if add >= 10:
result.append(add % 10)
tmp = add // 10
else:
result.append(add)
tmp = 0
l1 = l1.next
l2 = l2.next
while l1 != None and l2 == None:
add = l1.val + tmp
if add >= 10:
result.append(add % 10)
tmp = add // 10
else:
result.append(add)
tmp = 0
l1 = l1.next
while l2 != None and l1 == None:
add = l2.val + tmp
if add >= 10:
result.append(add % 10)
tmp = add // 10
else:
result.append(add)
tmp = 0
l2 = l2.next
if l1 == None and l2 == None and tmp > 0:
result.append(tmp)head = ListNode(0)
probe = head
for r in result:
probe.next = ListNode(r)
probe = probe.nextreturn head.next
"""
Runtime: 64 ms, faster than 91.78% of Python online submissions for Add Two Numbers.
Memory Usage: 11.7 MB, less than 5.16% of Python online submissions for Add Two Numbers.
"""
"""
第二次：将上述代码进行更简洁化处理，包括：①上述四种情况可以简化成一个while语句；②if-else语句可以在一行中实现；③新链表的建立可以在程序中实现；④原来分add大于等于10和小于10两种情况，其实根本不用分，此处可合并if-else语句
"""
# Definition for singly-linked list.
# class ListNode(object):
# def __init__(self, x):
# self.val = x
# self.next = Noneclass Solution(object):
def addTwoNumbers(self, l1, l2):
"""
:type l1: ListNode
:type l2: ListNode
:rtype: ListNode
"""
tmp = 0
head = ListNode(0)
probe = head
while l1 or l2:
x = l1.val if l1 else 0
y = l2.val if l2 else 0
add = x + y + tmp
probe.next = ListNode(add % 10)
tmp = add // 10
l1 = l1.next if l1 else 0
l2 = l2.next if l2 else 0
probe = probe.nextprobe.next = ListNode(tmp) if tmp else None
return head.next
"""
Runtime: 60 ms, faster than 99.41% of Python online submissions for Add Two Numbers.
Memory Usage: 11.8 MB, less than 5.16% of Python online submissions for Add Two Numbers.
"""