Palindrome Linked List 判断链表是否回文 栈实现

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:
//判断链表是否是回文：逆转比较，入栈比较；
    bool isPalindrome(ListNode* head) {
        
        stack<ListNode *> s;
        if(head==NULL)
            return true;
        ListNode *p=head;
        while(p!=NULL)
        {
            s.push(p);
            p=p->next;
        }
        
        bool f=true;
        p=head;
        while(!s.empty())
        {
            ListNode *tmp=s.top();
            if(p->val!=tmp->val)
            {
                f=false;
                break;
            }
            s.pop();
            p=p->next;
        }
        return f;
    }
};