Change the original code to include Switzerland in the map. Switzerland shares borders with France and Germany. No neighboring countries are the same color.

Suggested Answer

The code that has changed from color.cpp follows. You can view the complete program online in the file YourSolverHome/examples/src/color_ex4.cpp.

The declaration of the variables is changed as follows:

    IloIntVar Belgium(env, 0, 3), Denmark(env, 0, 3), France(env, 0, 3), 
      Germany(env, 0, 3), Luxembourg(env, 0, 3), Netherlands(env, 0, 3),
      Switzerland(env, 0, 3);

These additional constraints are added to the model

    model.add(France != Switzerland);
    model.add(Germany != Switzerland);

This code is added to the solution display:

      solver.out() << "Switzerland:  "
                   << Names[(IloInt)solver.getValue(Switzerland)] << endl;

You should obtain the following results:

FEASIBLE Solution
Belgium:     blue
Denmark:     blue
France:      white
Germany:     yellow
Luxembourg:  green
Netherlands: white
Switzerland: blue