/**

* Definition for singly-linked list.

* public class ListNode {

* int val;

* ListNode next;

* ListNode(int x) { val = x; }

* }

*/

public class Solution {

public ListNode oddEvenList(ListNode head) {

if (head == null)

return null;

ListNode newHead = head;

ListNode currOdd = head;

ListNode currEven = head.next;

ListNode evenHead = currEven;

while (currEven != null) {

if (currOdd.next == null || currOdd.next.next == null)

currOdd.next = evenHead;

else

currOdd.next = currOdd.next.next;

if (currEven.next != null)

currEven.next = currEven.next.next;

currOdd = currOdd.next;

currEven = currEven.next;

}

if (currOdd != evenHead)

currOdd.next = evenHead;

return newHead;

}

}