leetcode:(328) Odd Even Linked List (java)

package LeetCode_LinkedList;

/**
 * 题目：
 *      Given a singly linked list, group all odd nodes together followed by the even nodes.
 *      Please note here we are talking about the node number and not the value in the nodes.
 *      You should try to do it in place. The program should run in O(1) space complexity and O(nodes) time complexity.
 *      Example 1:
 *          Input: 1->2->3->4->5->NULL
 *          Output: 1->3->5->2->4->NULL
 *      Example 2:
 *          Input: 2->1->3->5->6->4->7->NULL
 *          Output: 2->3->6->7->1->5->4->NULL
 */
public class OddEvenList_328_1015 {
    public ListNode OddEvenList(ListNode head) {
        if (head == null || head.next == null) {
            return head;
        }
        ListNode odd = head;
        ListNode even = head.next;
        ListNode evenHead = even;

        while (even != null && even.next != null) {
            odd.next = even.next;
            odd = odd.next;

            even.next = odd.next;
            even = even.next;
        }
        odd.next = evenHead;
        return head;
    }

    public static void main(String[] args) {
        ListNode node1 = new ListNode(1);
        ListNode node2 = new ListNode(2);
        ListNode node3 = new ListNode(3);
        ListNode node4 = new ListNode(4);
        ListNode node5 = new ListNode(5);

        node1.next = node2;
        node2.next = node3;
        node3.next = node4;
        node4.next = node5;

        OddEvenList_328_1015 test = new OddEvenList_328_1015();
        ListNode result = test.OddEvenList(node1);

        while (result != null) {
            System.out.print(result.val + " ");
            result = result.next;
        }
    }
}