```
public class Solution {
public ListNode oddEvenList(ListNode head) {
if(head == null || head.next == null)
return head;
ListNode odd = head;
ListNode even = head.next;
ListNode evenHead = even;
while(odd.next != null && even.next != null){
odd.next = even.next;
odd = odd.next;
even.next = odd.next;
even = even.next;
}
odd.next = evenHead;
return head;
}
}
```