Odd Even Linked List

/**
 * 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 head;
        if (head.next == null || head.next.next == null)
            return head;
        ListNode fisrt = head;
        ListNode second = head.next;
        ListNode cur = second.next;
        ListNode fisrtTail = fisrt;
        ListNode secondTail = second;
        boolean nextIsFirst = true;
        while(cur !=null)
        {
            if( nextIsFirst)
            {
                fisrtTail.next = cur;
                fisrtTail = cur;
            }else{
                secondTail.next = cur;
                secondTail = cur;
            }
            nextIsFirst = (!nextIsFirst);
            cur = cur.next;
        }
        fisrtTail.next = second;
        secondTail.next = null;
        return fisrt;
    
    }
}