328.奇偶链表

 public ListNode oddEvenList(ListNode head) {
        if (head == null) {
            return null;
        }
        ListNode odd = head;
        ListNode evenhead = head.next;
        ListNode even = evenhead;
        while (even != null && even.next!= null) {
            odd.next = even.next;
            odd = odd.next;
            even.next = even.next.next;
            even = even.next;
        }
        odd.next = evenhead;
        return head;
    }