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

/** * 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
     
      vec;        ListNode *p = head;        int count = 0;        while(p)        {            count++;            p=p->next;        }        p = head;        if(count%2==0)          {              count/=2;              while(count--)              {                  vec.push_back(p->val);                  p=p->next;              }          }         else         {             count/=2;             while(count--)             {                 vec.push_back(p->val);                 p=p->next;             }             p=p->next;         }       reverse(vec.begin(),vec.end());       int i = 0;       while(p)       {           if(p->val!=vec[i])              return false;            p=p->next;            ++i;       }       return true;    }};