【LeetCode 234_链表】Palindrome Linked List

 ListNode* ReverseList(ListNode *p) {
     if (p == NULL || p->next == NULL)
         return p;

     ListNode *pre = NULL;
     ListNode *next = p->next;
     while (p) {
         p->next = pre;
         pre = p;
         p = next;
         next = p ? p->next : NULL;
     }
     return pre;
 }

 bool isPalindrome(ListNode* head) {
     if (head == NULL || head->next == NULL)
         return true;
     ListNode *slow = head, *fast = head;
     while (fast->next && fast->next->next) {
         slow = slow->next;
         fast = fast->next->next;
     }
     slow->next = ReverseList(slow->next);
     slow = slow->next;

     while (slow) {
         if (slow->val != head->val)
             return false;
         slow = slow->next;
         head = head->next;
     }
     return true;
 }