[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 || !(head -> next)) return true;
13         ListNode* slow = head;
14         ListNode* fast = head;
15         while (fast && fast -> next) {
16             slow = slow -> next;
17             fast = fast -> next -> next;
18         }
19         if (fast) {
20             slow -> next = reverseList(slow -> next);
21             slow = slow -> next;
22         }
23         else slow = reverseList(slow);
24         while (slow) {
25             if (head -> val != slow -> val)
26                 return false;
27             head = head -> next;
28             slow = slow -> next;
29         }
30         return true;
31     }
32 private:
33     ListNode* reverseList(ListNode* node) {
34         ListNode* pre = NULL;
35         while (node) {
36             ListNode* next = node -> next;
37             node -> next = pre;
38             pre = node;
39             node = next;
40         }
41         return pre;
42     }
43 };