【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;
}