【LeetCode】234. 回文链表

 1 /**
 2  * Definition for singly-linked list.
 3  * struct ListNode {
 4  *     int val;
 5  *     struct ListNode *next;
 6  * };
 7  */
 8 
 9 
10 int isPalindrome(struct ListNode* head){
11     struct ListNode *fast;
12     struct ListNode *slow;
13     struct ListNode *tmp;
14     struct ListNode *pre;
15     struct ListNode *cur;
16 
17     if( head == NULL || head->next == NULL )
18         return true;
19 
20     fast = head;
21     slow = head;
22 
23     // 分割链表
24     while( fast != NULL && fast->next != NULL )
25     {
26         slow = slow->next;
27         fast = fast->next->next;
28     }
29 
30     // cur指向链表后半部分的开头，如果是奇数个节点，则指向中心节点；
31     cur = slow;//slow->next;
32 
33     //printf("链表的后半部：");
34     //list_show( cur );
35 
36     // 原地反转后半部链表
37     pre = NULL;
38     while( cur != NULL )
39     {
40         tmp = cur->next;
41 
42         cur->next = pre;
43 
44         pre = cur;
45         cur = tmp;
46     }
47 
48     //printf("反转后的链表的后半部：");
49     //list_show( pre );
50 
51     // pre指向后半部链表反转后的开头
52     while( pre != NULL )
53     {
54         if( head->val != pre->val )
55             return false;
56 
57         pre = pre->next;
58         head = head->next;
59     }
60 
61     return true;
62 }