904. 加一链表
给定一个非负整数，这个整数表示为一个非空的单链表，每个节点表示这个整数的一位。返回这个整数加一。
除了0本身，所有数字在最高位前都没有0。
列表的头节点存的是这个整数的最高位。
样例
给出链表1 -> 2 -> 3 -> null，返回 1 -> 2 -> 4 -> null。
实现思路：
用数组和用链表两种方法
当使用链表时，先将链表翻转过来，然后加一以后再翻转
"""
Definition of ListNode
class ListNode(object):
def __init__(self, val, next=None):
self.val = val
self.next = next
"""
#用数组操作
class Solution:
"""
@param head: the first Node
@return: the answer after plus one
"""
def plusOne(self, head):
# Write your code here
#用数组操作
count = 0
cur = head
while cur:
count = count * 10 + cur.val
cur = cur.next
count += 1
dummy = ListNode(0)
pre = dummy
while count :
tmp = ListNode(count % 10)
tmp.next = pre.next
pre.next = tmp
count = count // 10
return dummy.next#用链表进行操作
class Solution:
"""
@param head: the first Node
@return: the answer after plus one
"""
def plusOne(self, head):
# Write your code here
#对链表进行翻转
new_head = None
while head:
tmp = head.next
head.next = new_head
new_head = head
head = tmp
head = new_head
carry = 1
new_head = None
while head:
tmp = head.next
head.next = new_head
new_head = head
head = tmp
val = new_head.val + carry
carry = val // 10
new_head.val = val % 10
if carry:
node = ListNode(carry)
node.next = new_head
new_head = node
return new_head