Odd Even Linked List

/**
 * 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:
    ListNode* oddEvenList(ListNode* head) {
        if (head == nullptr || head->next == nullptr) {
            return head; // No need to process if there are 0 or 1 nodes
        }

        ListNode* odd = head;
        ListNode* even = head->next;
        ListNode* evenHead = even; // Keep track of the start of even nodes
        int i = 0;

        while (odd->next != nullptr && even->next != nullptr) {
            if (i % 2 == 0) {
                odd->next = odd->next->next;
                if (odd->next != nullptr) {
                    odd = odd->next;
                }
            } else {
                even->next = even->next->next;
                if (even->next != nullptr) {
                    even = even->next;
                }
            }
            i++;
        }

        odd->next = evenHead; // Connect odd list with even list
        if (even != nullptr) {
            even->next = nullptr; // Terminate the even list
        }

        return head;
    }
};