Palindrome Linked List

Given a singly linked list, determine if it is a palindrome.

Follow up:
Could you do it in O(n) time and O(1) space?

 /**
  * Definition for singly-linked list.
  * struct ListNode {
  *     int val;
  *     ListNode *next;
  *     ListNode(int x) : val(x), next(NULL) {}
  * };
  */
 class Solution {
 public:
     bool isPalindrome(ListNode* head) {

         vector<int> tmp;
         while(head)
         {
             tmp.push_back(head->val);
             head=head->next;
         }
         int left=;
         int right=tmp.size()-;
         while(left<right)
         {
             if(tmp[left]!=tmp[right])
               return false;
             left++;
             right--;
         }
         return true;
     }
 };