LeetCode 234 Palindrome Linked List

 1 /*
 2     public class ListNode
 3     {
 4         int val;
 5         ListNode next;
 6 
 7         ListNode(int x)
 8         { val = x; }
 9     }
10 */
11 
12 import java.util.Stack;
13 
14 public class Solution
15 {
16     public boolean isPalindrome(ListNode head)
17     {
18         if(head == null || head.next == null)
19             return true;
20 
21         Stack<ListNode> stack = new Stack<>();
22         ListNode flag = head;
23 
24         while(flag != null)
25         {
26             stack.push(flag);
27             flag = flag.next;
28         }
29 
30         while(head != null)
31         {
32             if(head.val != stack.pop().val)
33                 return false;
34             head = head.next;
35         }
36 
37         return true;
38     }
39 }