/**

 * Definition for singly-linked list.

 * public class ListNode {

 *     int val;

 *     ListNode next;

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

 * }

 */

class Solution {

    public ListNode oddEvenList(ListNode head) {

        if (head == null || head.next == null || head.next.next == null) {

            return head;

        }

        ListNode head1 = new ListNode(-1);// 奇数链表

        ListNode head2 = new ListNode(-1);// 偶数链表

        ListNode p = head;

        ListNode p1 = head1;

        ListNode p2 = head2;

        for (int i = 0; p != null; i++) {

            if ((i & 1) == 0) {

                head1.next = p;

                head1 = head1.next;

            } else {

                head2.next = p;

                head2 = head2.next;

            }

            p = p.next;

        }

        head2.next = null;//偶数链表最后置为null

        head1.next = p2.next;

        return p1.next;

    }

}