解题思路：
O（1）的空间复杂度，意味着不能通过开一个List来解决问题。我们可以把List分成前后两个部分，后半部分通过指针的相互赋值进行翻转即可。
JAVA实现如下：
public static boolean isPalindrome(ListNode head) {
if (head == null || head.next == null)
return true;
ListNode middle = head, fast = head;
while (fast != null && fast.next != null) {
middle = middle.next;
fast = fast.next.next;
}
ListNode rightHalf = reverseListNode(middle);
while (rightHalf != null) {
if (rightHalf.val != head.val)
return false;
head = head.next;
rightHalf = rightHalf.next;
}
return true;
}
public static ListNode reverseListNode(ListNode head) {
if (head == null || head.next == null)
return head;
ListNode pre = head, cur = head.next, tmp = head;
head.next = null;
while (cur != null) {
tmp = cur.next;
cur.next = pre;
pre = cur;
cur = tmp;
}
return pre;
}
Java for LeetCode 234 Palindrome Linked List
原文：http://www.cnblogs.com/tonyluis/p/4934272.html