Partition List -- LeetCode

public ListNode partition(ListNode head, int x) {
    if(head == null)
        return null;
    ListNode helper = new ListNode(0);
    helper.next = head;
    ListNode walker = helper;
    ListNode runner = helper;
    while(runner.next!=null)
    {
        if(runner.next.val<x)
        {
            if(walker!=runner)
            {
                ListNode next = runner.next.next;
                runner.next.next = walker.next;
                walker.next = runner.next;
                runner.next = next;
            }
            else
                runner = runner.next;
            walker = walker.next;
        }
        else
        {
            runner = runner.next;
        }
    }
    return helper.next;
}