Handle the base cases
String x1 = " " ; String y1 = " " ; for ( int i = 0 ; i < Y ; i ++ ) { x1 += ' b ' ; } for ( int i = 0 ; i < X ; i ++ ) { y1 += ' a ' ; } if ( X == 0 ) return x1 ; if ( Y == 0 ) return y1 ;