Palindrome Linked List

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

 struct ListNode {     int val;     ListNode *next;     ListNode(int x) : val(x), next(NULL) {}};class Solution {public:     bool isPalindrome(ListNode *head) {        left = head;        return check(head);    }    bool check(ListNode *right)    {        if (right==nullptr)        {            return true;        }        bool result = check(right->next)&&(right->val==left->val);        left = left->next;        return result;    }private:    ListNode *left;};