234. Palindrome Linked List

Posted 2020-10-27 __Meng

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?

 

 

判断单链表是否是回文的

 

C++（25ms）：

 1 /**
 2  * Definition for singly-linked list.
 3  * struct ListNode {
 4  *     int val;
 5  *     ListNode *next;
 6  *     ListNode(int x) : val(x), next(NULL) {}
 7  * };
 8  */
 9 class Solution {
10 public:
11     ListNode* temp ;
12     bool isPalindrome(ListNode* head) {
13         temp = head ;
14         return check(head) ;
15     }
16     
17     bool check(ListNode* p){
18         if (p == NULL)
19             return true ;
20         bool flag = check(p->next) ;
21         flag = (p->val == temp->val) && flag ;
22         temp = temp->next ;
23         return flag ;
24     }
25 };