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?

1 /**
 2  * Definition for singly-linked list.
 3  * struct ListNode {
 4  *     int val;
 5  *     ListNode *next;
 6  *     ListNode(int x) : val(x), next(NULL) {}
 7  * };
 8  */
 9 class Solution {
10 public:
11     bool isPalindrome(ListNode* head) {
12         
13         vector<int> tmp;
14         while(head)
15         {
16             tmp.push_back(head->val);
17             head=head->next;
18         }
19         int left=0;
20         int right=tmp.size()-1;
21         while(left<right)
22         {
23             if(tmp[left]!=tmp[right])
24               return false;
25             left++;
26             right--;
27         }
28         return true;
29     }
30 };