[LeetCode]Reverse 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 == nullptr) return true;
13         
14         ListNode *slow = head;
15         ListNode *fast = head;
16         while (fast != nullptr && fast->next != nullptr) {
17             slow = slow->next;
18             fast = fast->next->next;
19         }
20         
21         // 逆序后一半链表
22         if (fast != nullptr) {
23             fast = reversedListedArray(slow->next);
24         } else {
25             fast = reversedListedArray(slow);
26         }
27         
28         slow = head;
29         while (slow != nullptr && fast != nullptr) {
30             if (slow->val != fast->val) {
31                 return false;
32             }
33             slow = slow->next;
34             fast = fast->next;
35         }
36         
37         return true;
38     }
39 private:
40     ListNode *reversedListedArray(ListNode *head) {
41         if (head == nullptr) return head;
42         
43         ListNode dummy(-1);
44         dummy.next = head;
45         ListNode *prev = dummy.next;
46         ListNode *cur = prev->next;
47         while (cur != nullptr) {
48             prev->next = cur->next;
49             cur->next = dummy.next;
50             dummy.next = cur;
51             cur = prev->next;
52         }
53         return dummy.next;
54     }
55 };