Method _find

chapter24/src/main/java/com/seaofnodes/simple/node/Node.java:727–735

(int nid, BitSet bs)

     */
    public Node find(int nid) { return _find(nid, new BitSet()); }
    private Node _find(int nid, BitSet bs) {
        if( bs.get(_nid) ) return null; // Been there, done that
        bs.set(_nid);
        if( _nid==nid ) return this;
        Node x;
        for( Node def : _inputs  )  if( def != null && (x = def._find(nid,bs)) != null ) return x;
        for( Node use : _outputs )  if( use != null && (x = use._find(nid,bs)) != null ) return x;
        return null;
    }
}