import java.util.*;


public class VectorSched
{
    protected Vector courses;
    protected Vector times;
    protected Vector constraintPairs;
    protected Hashtable mySchedule;

    public VectorSched() {
	courses = new Vector();
	times = new Vector();
	// this should be done with a Hashtable or a HashMap
	constraintPairs = new Vector();
	mySchedule = new Hashtable();
    }
    
    public void addCourse(String c) {
	courses.addElement(c);
    }
    public void addTimeSlot(String t) {
	times.addElement(t);
    }
    public void addConstraint(String c1, String c2) {
	constraintPairs.addElement(c1 + "/" + c2);
	constraintPairs.addElement(c2 + "/" + c1);
    }

    protected boolean allowed(String c1, String c2) {
	return(constraintPairs.indexOf(c1 + "/" + c2) < 0);
    }

    protected boolean allowed(String c1, Vector cx) {
	for(Enumeration e = cx.elements(); e.hasMoreElements(); ) {
	    String c2 = (String)(e.nextElement());
	    if (!allowed(c1,c2)) return false;
	}
	return true;
    }

    protected boolean scheduleOneCourse(int cNum, int tNum) {
	/* DEBUG
	System.out.println("Trying course " + cNum + " at time " + tNum);
	*/
	if (tNum >= times.size()) return false;
	String t = (String)(times.elementAt(tNum));
	if (cNum >= courses.size()) return true;
	String c = (String)(courses.elementAt(cNum));

	Vector cx = (Vector)(mySchedule.get(t));
	if (cx == null) {
	    cx = new Vector();
	    mySchedule.put(t,cx);
	}
	if (allowed(c,cx)) {
	    cx.addElement(c);
	}
	else return false;

	int nextc = cNum + 1;
	int nextt = (tNum + 1) % times.size();
	int ix;
	boolean gotit = false;
	
	// this approach will not always yield the most 
	// well spread-out schedule
	for(ix = 0; ix < times.size(); ix++) {
	    gotit = scheduleOneCourse(nextc, nextt);
	    if (gotit) break;
	    else nextt = (nextt + 1) % times.size();
	}

	if (!gotit) {
	    cx.removeElement(c);
	    return false;
	}
	else {
	    return true;
	}
    }

    public boolean schedule() {
	return scheduleOneCourse(0,0);
    }

    public String toString() {
	StringBuffer buf = new StringBuffer();
	for(Enumeration e = times.elements(); e.hasMoreElements(); ) {
	    String t = (String)(e.nextElement());
	    Vector cx = (Vector)(mySchedule.get(t));
	    buf.append("Time ");
	    buf.append(t);
	    buf.append(":  ");
	    if (cx != null && cx.size() > 0) {
		for(Enumeration e2 = cx.elements(); e2.hasMoreElements();){
		    buf.append(e2.nextElement().toString());
		    buf.append("  ");
		}
	    }
	    else buf.append("--free--");
	    buf.append("\n");
	}
	return buf.toString();
    }

}