Print all those elements whose presence is not marked .
for ( int i = 0 ; i < arr . Length ; i ++ ) if ( arr [ i ] > 0 ) Console . Write ( i + 1 + " ▁ " ) ; for ( int i = 0 ; i < helper . Length ; i ++ ) if ( helper [ i ] >= 0 ) Console . Write ( arr . Length + i + 1 + " ▁ " ) ; return ; }