回文链表

/*
struct ListNode {
    int val;
    struct ListNode *next;
    ListNode(int x) : val(x), next(NULL) {}
};*/
class Palindrome {
public:
    bool isPalindrome(ListNode* pHead) {
        ListNode* slow = pHead, *fast = pHead;
        stack<int> s;
        //注意对快指针的边界判断！！        
　　　　　　　while(fast != NULL && fast->next != NULL) {
            s.push(slow->val);
            slow = slow->next;
            fast = fast->next->next; 
        }
        //奇数个元素
        if(fast != NULL) 
            slow = slow->next;
        while(slow != NULL) {
            if (slow->val == s.top()) {
                slow = slow->next;
                s.pop();
            }
            else
                return false;
        }
        return true;

    }
};