public void removeLines(){
        for (int i = 0; i < HEIGHT; i++){
            boolean rowNotFull = false;
            for (int j = 0; j < WIDTH; j++){
                if (!playground[i][j]){
                    rowNotFull = true;
                    break;
                }
            }
            if (!rowNotFull)
                clearRow(i);
        }
    }