71 problem

/*
 * File: practice.java
 * Name:
 * Section Leader:
 * --------------------
 * This file is the starter file for the Hailstone problem.
 */

import acm.graphics.GCanvas;
import acm.graphics.GLabel;
import acm.graphics.GLine;
import acm.program.*;
import java.util.*;
import java.awt.event.*;
import javax.swing.*;

public class Practice extends GraphicsProgram {
	public Practice() {

	}

	public void addTeacher(String teacher) {
		teachers.add(teacher);
	}

	public void addSubject(String teacher, String subject) {
		if (teachers.contains(teacher)) {
			ArrayList<String> sub;
			sub = Tsubjects.get(teacher);
			sub.add(subject);
			Tsubjects.put(teacher,sub);

			ArrayList<String> teach;
			teach = Steachers.get(subject);
			teach.add(teacher);
			Steachers.put(subject, teach);
		}
	}

	public void addPupil(String pupil, String subject) {
		if (pupils.contains(pupil)) {
			pupils.add(pupil);
			ArrayList<String> pup;
			pup = Spupils.get(subject);
			pup.add(pupil);
			Spupils.put(subject,pup);


			ArrayList<String> sub;
			sub = Psubjects.get(pupil);
			sub.add(subject);
			Psubjects.put(pupil,sub);
		}
	}

	public Iterator<String> getTeachers(String pupil) {
		if (pupils.contains(pupil)) {
			ArrayList <String> temp;
			ArrayList <String> answer = new ArrayList <String>();
			temp=Psubjects.get(pupil);
			for (int i=0;i<temp.size();i++) {
				if (Steachers.get(temp.get(i))!=null) {
					mergeArr(answer,Steachers.get(temp.get(i)));
				}
			}
			for (int i=0;i<answer.size();i++) {
				if (!teachers.contains(answer.get(i))) {
					answer.remove(i);
				}
			}
			return answer.iterator();
		}
		return null;
	}

	private void mergeArr (ArrayList a,ArrayList b) {
		for (int i=0;i<b.size();i++) {
			if (!a.contains(b.get(i))) {
				a.add(b.get(i));
			}
		}
	}
	public Iterator<String> getPupils(String teacher) {
		if (teachers.contains(teacher)) {
			ArrayList <String> temp;
			ArrayList <String> answer = new ArrayList <String>();
			temp=Tsubjects.get(teacher);
			for (int i=0;i<temp.size();i++) {
				if (Spupils.get(temp.get(i))!=null) {
					mergeArr(answer,Spupils.get(temp.get(i)));
				}
			}
			return answer.iterator();
		}
		return null;
	}

	public void removeTeacher(String teacher) {
		for (int i=0;i<teachers.size();i++) {
			if (teachers.get(i).equals(teacher)) {
				teachers.remove(i);
			}
		}
		Tsubjects.remove(teacher);

	}
	ArrayList <String> teachers;
	Map < String,ArrayList<String> > Tsubjects = new HashMap < String,ArrayList<String> >();
	ArrayList <String> pupils;
	Map < String,ArrayList<String> > Spupils = new HashMap < String,ArrayList<String> >();
	Map < String,ArrayList<String> > Psubjects = new HashMap < String,ArrayList<String> >();
	Map < String,ArrayList<String> > Steachers = new HashMap < String,ArrayList<String> >();
}