Getting started

Consider the problem of graph coloring as depicted in Fig. 1.1. Below, we provide a simplistic program with hard-coded constraints and specification of the search method to solve this particular graph coloring problem.

import org.jacop.core.*;
import org.jacop.constraints.*;
import org.jacop.search.*;

public class Main {

    static Main m = new Main ();

    public static void main (String[] args) {
        Store store = new Store();  // define FD store
        int size = 4;
        // define finite domain variables
        IntVar[] v = new IntVar[size];
        for (int i=0; i<size; i++)
            v[i] = new IntVar(store, "v"+i, 1, size);
        // define constraints
        store.impose( new XneqY(v[0], v[1]) );
        store.impose( new XneqY(v[0], v[2]) );
        store.impose( new XneqY(v[1], v[2]) );
        store.impose( new XneqY(v[1], v[3]) );
        store.impose( new XneqY(v[2], v[3]) );

        // search for a solution and print results
        Search<IntVar> search = new DepthFirstSearch<IntVar>();
        SelectChoicePoint<IntVar> select =
            new InputOrderSelect<IntVar>(store, v,
                                         new IndomainMin<IntVar>());
        boolean result = search.labeling(store, select);

        if ( result )
            System.out.println("Solution: " + v[0]+", "+v[1] +", "+
                                              v[2] +", "+v[3]);
        else
            System.out.println("*** No");
    }
}

This program produces the following output indicating that vertices v0, v1 and v3 get different colors (1, 2 and 3 respectively), while vertex v3 is assigned color number 1.

1.1 Getting started