private ListNode    insertHelper(ListNode head) {
        ListNode    dum =  new ListNode(-999999);
        
        ListNode    p1  =  head;    
        while ( p1 != null ) {
            ListNode    _p1  =  p1.next;
            ListNode    pre2  =  dum;
            ListNode      p2  =  dum.next;
            while ( p2 != null ) {
                if ( p2.val > p1.val ) {
                    pre2.next  =  p1;
                    p1.next  =  p2;
                    break;
                }
                pre2  =  pre2.next;
                p2    =  p2.next;
            }
            if ( p2 == null ) {
                pre2.next  =  p1;
                p1.next  =  p2;
            }
            p1  =  _p1;    
        }
        return dum.next;
    }