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leetcode 0234

admin 11月 13, 2020 0

Desicription

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

Example 1:

1 2	Input: 1->2 Output: false

Example 2:

1 2	Input: 1->2->2->1 Output: true

Follow up:

Could you do it in O(n) time and O(1) space?

Solution


 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class  {
private:
    ListNode* tmp = nullptr;
    bool check(ListNode* p) {
        if(nullptr == p) {
            return true;
        }
        bool flag = check(p->next) && (p->val == tmp->val);
        tmp = tmp->next;
        return flag;
    }
public:
    bool isPalindrome(ListNode* head) {
        tmp = head;
        return check(head);
    }
};