题目：
Given a singly linked list, determine if it is a palindrome. Follow up: Could you do it in O(n) time and O(1) space?
碉堡！
reference：http://www.cnblogs.com/grandyang/p/4635425.html
题目：
Given a singly linked list, determine if it is a palindrome. Follow up: Could you do it in O(n) time and O(1) space?
碉堡！
reference：http://www.cnblogs.com/grandyang/p/4635425.html