question: private String formatNode ( SegmentTreeNode < ? > node ) { StringBuilder response = new StringBuilder ( "(" ) ; if ( node . lson != null ) { response . append ( formatNode ( node . lson ) ) ; } response . append ( node . toString ( ) ) ; if ( node . rson != null ) { response . append ( formatNode ( node . rson ) ) ; } response . append ( ")" ) ; return response . toString ( ) ; }
target:  Format the node, recursively.