https://leetcode.com/problems/palindrome-linked-list/
understanding
这里涉及given a head node, find the middle point of a linked list.
要注意
1， 找到middle point之后，不需要分奇数和偶数长度，只需要知道middle.next肯定就是要reversed的linked list的head
2. reverse之后，只需要一个从头一个从尾，逐个比较就行，直到某一个指针指向None。
ref:
http://bookshadow.com/weblog/2015/07/10/leetcode-palindrome-linked-list/
my code:
class Solution(object):
def isPalindrome(self, head):
"""
:type head: ListNode
:rtype: bool
"""
i, j= head, head
if not head:
return True
if not head.next:
return True
while i.next and i.next.next:
i = i.next.next
j = j.next
cur, pre = j.next, None # pre can get the head node of the reversed linkedlist
while cur:
next_node = cur.next
cur.next = pre
pre, cur = cur, next_node
new_head = pre
p1,p2 = head, new_head
while p1 and p2 and p1.val == p2.val:
p1,p2 = p1.next, p2.next
if not p1 or not p2:
return True
else:
return False
