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In this lab we will design two different ways to represent 
a transit system. We will then design methods for the system,
such as finding all stations on a given route, or finding
a route from one station to another.

The goals are:
  experience how the way the data is represented affects the
    design of methods that process the data

  understand the distinction between information and its 
    representation as classes of data

  recall and practice writing methods using the accumulator
    style - and understand the need for accumulators
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Problem statement:
The information about the city transit system allows the passengers
to find out about the routes and stations and schdules. We are asked
to design this computerized system.

For each station we need to record the name, and its location.
Each of the train routes has a name and a color.
For each route segment between two stations, we need to know the
origin and destination, the route that connects them, and the time
it takes to travel from one station to another.
The transit system record all this information.

We impose two restrictions on the system as follows: 
1. There are at most two routes that lead from any given station 
   to another station.

2. It is impossible to travel through the same station twice
   in one trip. 


Here is a sample transit system:


Sample big transit:

           A
         /   \
        /     \
       /       \
      /         \   
     B           C
    / \         / \
   /   \       /   \
  F     G     S     E 
  \    / \   /|    /
   |  /   \ / |   /
   | H     K  |  N
   |      / \ | / \
    \    /   \|/   \
     \  /     P     T
      Z

Blue:    A -5- B -3- F -8- Z
Red:     A -3- C -4- S -5- K -3- Z
Green:   B -2- G -5- K -3- P
Yellow:  C -3- E -4- N -5- P
White:   G -4- H
Black:   N -3- T     S -6- P

You may want to draw a color picture, to better understand the 
available information. Here is another, simpler system we will work
with at the beginning:

Sample simple transit:

     B          
    / \       
   /   \     
  F     G   
  \    / \  
   |  /   \
   | H     K 
   |      / \ 
    \    /   \
     \  /     P    
      Z

Blue:    B -3- F -8- Z
Green:   B -2- G -5- K -3- P
Red:     K -3- Z
White:   G -4- H

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Here is another data definition for this system:

OneStop is a structure
  Route   route
  int     minutes
  Station origin
  Station destination

Station consists of
  String    name
  Posn      loc

Route is a structure
  String name
  Color color

Transit is a list of OneStop-s
 
We give you the class definitions, mainly because the implementation
of the 'same' method needed for comparisons and test cases is 
tedious. However, you need to complete the design of these classes
by making examples of data that represent the simple transit 
system.

Design these classes and make examples of data for the simple transit
system. To simplify the equality comparison, add the following method
to the class OneStep:


  String makeString(){
   return "* ".concat(this.route.name).concat(" from: ")
              .concat(this.origin.name).concat("  to: ")
              .concat(this.destination.name).concat(" *");

and add a similar method to the classes that represent the transit.

Compare any two lists of OneStop by comparing the resulting String-s.

Finally, design the mehtod that produces a list of stations that 
follow after the given station in this transit on any of the routes.
Notice, that while in the previous class hierarchy knowing which
station we are at was sufficient to find all next stations, here we
need to query the whole transit system.

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