class PalindromeList {
public:
    struct ListNode* middleNode(struct ListNode* head) {
        struct ListNode* slow = head;
        struct ListNode* fast = head;
        while (fast && fast->next)
        {
            slow = slow->next;
            fast = fast->next->next;
        }
        return slow;
    }
    struct ListNode* reverseList(struct ListNode* head) {
        struct ListNode* n1 = NULL;
        struct ListNode* n2 = head;
        struct ListNode* n3 = NULL;
        while (n2)
        {
            n3 = n2->next;
            n2->next = n1;
            n1 = n2;
            n2 = n3;
        }
        return n1;
    }
    bool chkPalindrome(ListNode* A) {
        // write code here
        struct ListNode* mid = middleNode(A);
        struct ListNode* rmid = reverseList(mid);
        while (A && rmid)
        {
            if (A->val != rmid->val)
                return false;
            else
            {
                A = A->next;
                rmid = rmid->next;
            }
        }
        return true;
    }
};
class Partition {
public:
    ListNode* partition(ListNode* pHead, int x) {
        // write code here
        struct ListNode* lessGuard, * lessTail, * graterGuard, * graterTail;
        lessGuard = lessTail = (struct ListNode*)malloc(sizeof(struct ListNode));
        graterGuard = graterTail = (struct ListNode*)malloc(sizeof(struct ListNode));
        lessGuard->next = NULL;
        graterGuard->next = NULL;

        struct ListNode* cur = pHead;
        while (cur)
        {
            if (cur->val < x)
            {
                lessTail->next = cur;
                lessTail = lessTail->next;
            }
            else
            {
                graterTail->next = cur;
                graterTail = graterTail->next;
            }
            cur = cur->next;
        }

        lessTail->next = graterGuard->next;
        graterTail->next = NULL;

        pHead = lessGuard->next;
        free(graterGuard);
        free(lessGuard);

        return pHead;
    }