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leet code: 1209 - Palindrome Linked List

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/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    bool isPalindrome(ListNode* head) {
        ListNode* newHead = new ListNode();
        int nodeLen = getLength(head);
        int halfLen = (nodeLen+1) / 2;
        int halfLen1 = nodeLen / 2;

        ListNode* fakeHead1 = new ListNode();
        ListNode* fakeHead2 = new ListNode();
        fakeHead1->next = fakeHead2;
        fakeHead2->next = head;
        ListNode* ptr = head;
        ListNode* ptr2 = fakeHead1;

        // reverse sort by halfLen
        for (int i = 0; i < halfLen; ++i)
        {
            fakeHead2->next = ptr->next;
            ptr->next = fakeHead1->next;
            fakeHead1->next = ptr;

            ptr = fakeHead2->next;
            ptr2 = ptr2->next;
        }

        // compare along fakeHead1, fakeHead2
        fakeHead1 = fakeHead1->next;
        if (nodeLen % 2 == 1)
            fakeHead1 = fakeHead1->next;
        fakeHead2 = fakeHead2->next;
        for (int i = 0; i < halfLen1; ++i)
        {
            if (fakeHead1->val != fakeHead2->val)
            {
                return false;
            }
            fakeHead1 = fakeHead1->next;
            fakeHead2 = fakeHead2->next;
        }
        return true;
    }
private:
    int getLength(ListNode* head)
    {
        int len = 0;
        while (head != nullptr)
        {
            head = head->next;
            len++;
        }
        return len;
    }
};