leetcode -Palindrome Linked List

 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     bool isPalindrome(ListNode* head) {
12         if(head == NULL || head->next == NULL) return true;
13         if(head->next->next == NULL){
14             if(head->val == head->next->val) return true;
15             else return false;
16         }
17         ListNode* tp1 = head;
18         ListNode* tp2 = head;
19         while(tp2->next != NULL && tp2->next->next != NULL){
20             tp1 = tp1->next;
21             tp2 = tp2->next->next;
22         }
23         ListNode* mid = tp1->next;
24         ListNode* p1 = head;
25         ListNode* p2 = reverse(mid);
26         while(p2 != NULL){
27             if(p2->val != p1->val) return false;
28             else{
29                 p1 = p1->next;
30                 p2 = p2->next;
31             }
32         }
33         return true;
34     }
35     ListNode* reverse(ListNode* mid){
36         if(mid->next == NULL) return mid;
37         ListNode* now = mid;
38         ListNode* prev = NULL;
39         while(now != NULL){
40             ListNode* tp = now->next;
41             now->next = prev;
42             prev = now;
43             now = tp;
44         }
45         return prev;
46     }
47 };