LeetCode 0328 - Odd Even Linked List

Input: 1->2->3->4->5->NULL
Output: 1->3->5->2->4->NULL

Input: 2->1->3->5->6->4->7->NULL
Output: 2->3->6->7->1->5->4->NULL

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* oddEvenList(ListNode* head) {
        if(head == nullptr) {
            return nullptr;
        }
        auto odd = head;
        auto even = head->next;
        auto evenHead = even;
        while(even != nullptr && even->next != nullptr) {
            odd->next = odd->next->next;
            even->next = even->next->next;
            odd = odd->next;
            even = even->next;
        }
        odd->next = evenHead;
        return head;
    }
};