234. Palindrome Linked List

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public boolean isPalindrome(ListNode head) {
        if(head==null) return true;
        if(head.next==null) return true;
        ListNode fast = head;
        ListNode slow = head;
        ListNode reverse = null;
        while(fast.next!=null && fast.next.next!=null) {
            fast = fast.next.next;
            slow = slow.next;
            head.next = reverse;
            reverse = head;
            head = slow;
        }
        slow = slow.next;
        if(fast.next == null) {
            head = reverse;
        }else {
            head.next = reverse;
        }

        //System.out.println(head.val);
        while(head !=null && slow !=null) {
            if(head.val == slow.val) {
                head = head.next;
                slow = slow.next;
            }
            else return false;
        }
        return true;
        
        
    }
}