[LeetCode]Palindrome Linked List

/**
* Definition for singly-linked list.
* public class ListNode {
*     int val;
*     ListNode next;
*     ListNode(int x) { val = x; }
* }
*/
public class Solution {
public boolean isPalindrome(ListNode head) {
if (head == null || head.next == null) {
return true;
}
int length = 0;
ListNode p = head;
while (p != null) {
length ++;
p = p.next;
}
p = head;
ListNode pre = p;
for (int i = 0; i < length / 2; i++) {
pre = p;
p = p.next;
}
if (length % 2 == 0) {
pre.next = null;
p = reverse(p);
} else {
pre.next = null;
p = p.next;
p = reverse(p);
}
while (head != null) {
if (head.val != p.val) {
return false;
}
head = head.next;
p = p.next;
}
return true;
}
public ListNode reverse(ListNode head) {
ListNode p2 = head;
ListNode p1 = null;
while (p2 != null) {
ListNode tmp = p2;
p2 = p2.next;
tmp.next = p1;
p1 = tmp;
}
return p1;
}
}