PlaindromeList.java

/**
 * 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;
        
        ListNode faster = head;
        Stack<Integer> values = new Stack<Integer>();
        
        // Reach the middle with head
        while (faster.next != null && faster.next.next != null) {
            values.push(head.val);
            faster = faster.next.next;
            head = head.next;
        }
        
        // Check if push the middle element or not
        if (faster.next != null) {
            values.push(head.val);
        }
        
        while (head.next != null) {
            head = head.next;
            if (head.val != values.pop()) {
                return false;
            }
        }
        
        return true;
    }
}