234. Palindrome Linked List LeetCode

class Solution {
public:
ListNode* reverseList(ListNode* head) {
ListNode *pre = NULL;
ListNode *cur = head;
while(cur != NULL)
{
ListNode *next = cur->next;
cur->next = pre;
pre = cur;
cur = next;
}
return pre;
}
bool isPalindrome(ListNode* head) {
ListNode* slow,* fast;
slow = fast = head;
while(fast && fast->next)
{
slow = slow->next;
fast = fast->next->next;
}
if(fast)
{
slow->next = reverseList(slow->next);
slow = slow->next;
}
else
slow = reverseList(slow);
while(slow)
{
if(slow->val != head->val) return false;
slow = slow->next;
head = head->next;
}
return true;
}
};