lab 108

Lab108-VenbergGE/src/PrevAssignmentClasses/AbstractBinaryTree.java

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+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+/*
+ *  * Data Structures & Algorithms 6th Edition 
+ * Goodrich, Tamassia, Goldwasser
+ * Code Fragments 8.7, 8.26, 8.22
+ *\
+
+/**
+ * an abstract base class providing some functionality of the binarytree interface
+ * @author Gabriel Venberg
+ */
+public abstract class AbstractBinaryTree<E> extends AbstractTree<E> implements BinaryTree<E> {
+	public Position<E> sibling(Position<E> p){
+		Position<E> parent = parent(p);
+		//p is root.
+		if (parent == null){return null;}
+		//p is left child, right child might be null.
+		if (p==left(parent)){return right(parent);}
+		//p is right child, left child might be null.
+		else {return left(parent);}
+	}
+	
+	/**returns the number of children of Position p*/
+	public int numChildren(Position<E> p){
+		int count=0;
+		if (left(p)!=null){count++;}
+		if(right(p)!=null){count++;}
+		return count;
+	}
+	
+	/**returns an iterable collection of Positions representing p's children.*/
+	public Iterable<Position<E>> children(Position<E> p){
+		//max capacity of 2
+		List <Position<E>> snapshot=new ArrayList<>(2);
+		//needed to modify this, as the arraylist we made in class needed an index
+		if(left(p)!=null){snapshot.add(left(p));}
+		if(right(p)!=null){snapshot.add(right(p));}
+		// and our arraylist 
+		return snapshot;
+	}
+	
+	/**adds positions of the subtree rooted at Position p to the given snapshot*/
+	private void inorderSubtree(Position<E> p, List<Position<E>> snapshot){
+		if(left(p)!=null){inorderSubtree(left(p), snapshot);}
+		snapshot.add(p);
+		if(right(p)!=null){inorderSubtree(right(p), snapshot);}
+	}
+	
+	/**returns an iterable collection of the positions of the tree, reported in inorder.*/
+	public Iterable<Position<E>> inorder(){
+		List<Position<E>> snapshot=new ArrayList<>();
+		//fill snapshot recursively
+		if(!isEmpty()){inorderSubtree(root(), snapshot);}
+		return snapshot;
+	}
+	
+	/**Overrides positions to make inorder the default order for binary trees*/
+	public Iterable<Position<E>> positions(){
+		return inorder();
+	}
+	
+			//nested ElementIterator class
+		/**this class adapts the iteration produced by positions() to returns elements*/
+		private class ElementIterator implements Iterator<E>{
+			Iterator<Position<E>> posIterator=positions().iterator();
+			public boolean hasNext(){return posIterator.hasNext();}
+			//return element
+			public E next(){return posIterator.next().getElement();}
+			public void remove(){posIterator.remove();}
+		}//end of nested ElementIterator class
+		
+		/**returns an iterator if the elements stored in the tree*/
+		public Iterator<E> iterator(){return new ElementIterator();}
+}

Lab108-VenbergGE/src/PrevAssignmentClasses/AbstractTree.java

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+
+import java.util.ArrayList;
+import java.util.List;
+
+/*
+ *  * Data Structures & Algorithms 6th Edition 
+ * Goodrich, Tamassia, Goldwasser
+ * Code Fragments 8.2-8.5, 8.19-21
+ *\
+/*
+ * an abstract base class providing some functionality of the tree interface.
+ * @author Gabriel Venberg
+ */
+public abstract class AbstractTree<E> implements Tree<E> {
+	public boolean isInternal(Position<E> p) {return numChildren(p)>0;}
+	public boolean isExternal(Position<E> p){return numChildren(p)==0;}
+	public boolean isRoot(Position<E> p){return p == root();}
+	public boolean isEmpty(){return size()==0;}
+
+	/**returns the number of levels sperating position p from the root.*/
+	public int depth(Position<E> p){
+		if (isRoot(p)){return 0;}
+		else{return 1+depth(parent(p));}
+	}
+
+	/**returns the hight of the tree.*/
+	private int hightBad(){ //works, but quadratic worst case time.
+		int h=0;
+		for(Position<E> p : positions()){
+			//only consider leaf positions.
+			if(isExternal(p)){h=Math.max(h, depth(p));}
+		}
+		return h;
+	}
+
+	/**returns the hight of the subtree rooted at position p.*/
+	public int hight(Position<E> p){
+		//base case if p is external
+		int h=0;
+		for (Position<E> c : children(p)){
+			h=Math.max(h,1+hight(c));
+		}
+		return h;
+	}
+	
+	//iterators
+	/**adds positions of the subtree rooted at position p to the given snapshot (for use in traversal)*/
+	private void preorderSubtree(Position<E> p, List<Position<E>> snapshot){
+		//for preorder, add position p before exploring subtrees.
+		snapshot.add(p);
+		for(Position<E> c:children(p)){
+			preorderSubtree(c, snapshot);
+		}
+	}
+	
+	/**returns an iterable collection of positions in the tree, reported in preorder*/
+	public Iterable<Position<E>> preorder(){
+		List<Position<E>> snapshot=new ArrayList<>();
+		//fill the snapshot recursively
+		if(!isEmpty()){
+			preorderSubtree(root(), snapshot);
+		}
+		return snapshot;
+	}
+	
+	/**adds positions of the subtree rooted at position p to the given snapshot (for use in traversal)*/
+	private void postorderSubtree(Position<E> p, List<Position<E>> snapshot){
+		//for postorder, add position p before exploring subtrees.
+		for(Position<E> c:children(p)){
+			postorderSubtree(c, snapshot);
+		}
+		snapshot.add(p);
+	}
+	
+	/**returns an iterable collection of positions in the tree, reported in postorder*/
+	public Iterable<Position<E>> postorder(){
+		List<Position<E>> snapshot=new ArrayList<>();
+		//fill the snapshot recursively
+		if(!isEmpty()){
+			postorderSubtree(root(), snapshot);
+		}
+		return snapshot;
+	}
+	
+	/**returns an iterable collection of positions in the tree in breadth first traversal*/
+	public Iterable<Position<E>> breadthFirst(){
+		List<Position<E>> snapshot=new ArrayList<>();
+		if(!isEmpty()){
+			Queue<Position<E>> fringe=new LinkedQueue<>();
+			fringe.enqueue(root());
+			while(!fringe.isEmpty()){
+				Position<E> p=fringe.dequeue();
+				snapshot.add(p);
+				for(Position<E> c:children(p)){
+					fringe.enqueue(c);
+				}
+			}
+		}
+		return snapshot;
+	}
+	
+	/**default iterator*/
+	public Iterable<Position<E>> positions(){return preorder();}
+}

Lab108-VenbergGE/src/PrevAssignmentClasses/ArrayQueue.java

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+/*
+ * Data Structures & Algorithms 6th Edition 
+ * Goodrich, Tamassia, Goldwasser
+ * Code Fragment 6.10
+ * 
+ * An implementation of the ArrayQueue class
+ * */
+
+/**
+ *implementation of the queue ADT using a fixed-length array.
+ * @author Gabriel Venberg
+ */
+public class ArrayQueue<E> implements Queue<E>{
+    //instance variables
+    private E[] data;   //generic array used for storage
+    private int f = 0;  //index of the front element
+    private int sz = 0;   //current number of elements
+    private static final int CAPACITY = 1000; //default capacity, book is missing this.
+    
+    //constructors
+    /** constructs queue with default capacity*/
+    public ArrayQueue(){this(CAPACITY);}
+    /**constructs queue with given capacity*/
+    public ArrayQueue(int capacity){
+        data = (E[]) new Object[capacity];
+    }
+    
+    //methods
+    /** returns the number of elements in the queue*/
+    public int size(){return sz;}
+    
+    /** tests whether the queue is empty*/
+    public boolean isEmpty(){return sz == 0;}
+    
+    /**inserts an element at the rear of the queue*/
+    public void enqueue(E e) throws IllegalStateException{
+        if(sz==data.length){throw new IllegalStateException("queue is full");}
+        int avail = (f+sz)%data.length; //use modular arithmatic
+        data[avail]=e;
+        sz++;
+    }
+    
+    /** returns but does not remove the first element in the queue or null if emtpy*/
+    public E first(){
+        if(isEmpty()){return null;}
+        return data[f];
+    }
+    
+    /** removes and returns the first element of the queue or null if emtpy*/
+    public E dequeue(){
+        if(isEmpty()){return null;}
+        E answer = data[f];
+        data[f]=null; //dereference to help GC
+        f=(f+1)%data.length;
+        sz--;
+        return answer;
+    }
+}

Lab108-VenbergGE/src/PrevAssignmentClasses/ArrayStack.java

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+/*
+ * Data Structures & Algorithms 6th Edition 
+ * Goodrich, Tamassia, Goldwasser
+ * Code Fragment 6.2
+ * 
+ * An implementation of an ArrayStack class
+ * */
+
+/**
+ *
+ * @author Gabriel Venberg
+ */
+public class ArrayStack<E> implements Stack<E> {
+    public static final int CAPACITY = 1000;//default capacity
+    private E[] data;       //generic array used for storage.
+    private int t=-1;       //index of the top element in the stack
+    
+    
+    //im swiching the authors comments to javadoc style, for ease of use.
+    
+    /**
+     * constructs stack with default capacity
+     */
+    public ArrayStack(){this(CAPACITY);}
+    
+    /**
+     * constructs stack with given capacity
+     * @param capacity capacity to construct the stack with.
+     */
+    public ArrayStack(int capacity){
+        data = (E[]) new Object[capacity];
+    }
+    
+    public int size(){return (t+1);}
+    
+    public boolean isEmpty(){return(t==-1);}
+    
+    public void push(E e) throws IllegalStateException{
+        if(size()==data.length){throw new IllegalStateException("Stack is full");}
+        data[++t]=e; //increment t before storing a new item.
+    }
+    
+    public E top(){
+        if(isEmpty()){return null;}
+        return data[t];
+    }
+    
+    public E pop(){
+        if(isEmpty()){return null;}
+        E answer = data[t];
+        data[t] = null; //dereference to help with garbage collection.
+        t--;
+        return answer;
+    }
+}

Lab108-VenbergGE/src/PrevAssignmentClasses/BinaryTree.java

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+/*
+ *  * Data Structures & Algorithms 6th Edition 
+ * Goodrich, Tamassia, Goldwasser
+ * Code Fragments 8.6
+ *\
+
+\**
+ *an interface for a binary tree, in which each node has at most two children.
+ * @author Gabriel Venberg
+ */
+public interface BinaryTree<E> extends Tree<E> {
+	/**returns the position of p's left child (or null if no child exists).*/
+	Position<E> left(Position<E> p) throws IllegalArgumentException;
+	/**returns the position of p's right child (or null if no child exists)*/
+	Position<E> right(Position<E> p) throws IllegalArgumentException;
+	/**returns the position of p's sibling (or null of no sibling exists).*/
+	Position <E> sibling(Position<E> p) throws IllegalArgumentException;
+}

Lab108-VenbergGE/src/PrevAssignmentClasses/LinkedBinaryTree.java

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+/*
+ *  * Data Structures & Algorithms 6th Edition 
+ * Goodrich, Tamassia, Goldwasser
+ * Code Fragments 8.9-11
+ *\
+
+/**
+ *
+ * @author Gabriel Venberg
+ */
+public class LinkedBinaryTree<E> extends AbstractBinaryTree<E> {
+	
+	//nested node class
+	protected static class Node<E> implements Position<E>{
+		//an element stored at this node
+		private E element;
+		//a reference the the parent node
+		private Node<E> parent;
+		//a refrence to the left node
+		private Node<E> left;
+		//a reference the right node
+		private Node<E> right;
+		
+		/**constructs a done with the given element and neighbors*/
+		public Node(E e, Node<E> above, Node<E> leftChild, Node<E> rightChild){
+			element=e;
+			parent=above;
+			left=leftChild;
+			right=rightChild;
+		}
+		
+		//why do we set the variables to private and make these methods for a protected class? doesnt that add uneeded overhead for no benifits of encapsulation?
+		//acessor methods
+		public E getElement(){return element;}
+		public Node<E> getParent(){return parent;}
+		public Node<E> getLeft(){return left;}
+		public Node<E> getRight(){return right;}
+		
+		//update methods
+		public void setElement(E e){element=e;}
+		public void setParent(Node<E> parentNode){parent=parentNode;}
+		public void setLeft(Node<E> leftChild){left=leftChild;}
+		public void setRight(Node<E> rightChild){right=rightChild;}
+	}//end of node class.
+	
+	//why create this class? its the exact same as just using the node constructor, even the same signature!
+	/**factory function to create new node storing element e*/
+	protected Node<E> createNode(E e, Node<E> parent, Node<E> left, Node<E> right){
+		return new Node<E>(e, parent, left, right);
+	}
+	
+	//LinkedBinaryTree instance variables
+	//root of the tree
+	protected Node<E> root=null;
+	//number of nodes in the tree
+	private int size=0;
+	
+	//constructor
+	//creats an empty binary tree
+	public LinkedBinaryTree(){}
+	
+	//nonpublic utility
+	/**validates the position and returns it as a node*/
+	protected Node<E> validate(Position<E> p) throws IllegalArgumentException{
+		if(!(p instanceof Node)){
+			throw new IllegalArgumentException("not a valid position type");
+		}
+		//safe cast
+		Node<E> node=(Node<E>)p;
+		//our convention for a defunct node. Wont this make the GC not clean it up? why not just set the parent to null and let the GC clean it up?
+		if(node.getParent()==node){
+			throw new IllegalArgumentException("p is no longer in the tree");
+		}
+		return node;
+	}
+	
+	//acessor methods still left to implement
+	/**returns the number of nodes in the tree*/
+	public int size(){return size;}
+	
+	/**returns the root position of the tree (or null if tree is empty)*/
+	public Position<E> root(){return root;}
+	
+	/**returns the position of p's parent or null if p is root*/
+	public Position<E> parent(Position<E> p) throws IllegalArgumentException {
+		Node<E> node=validate(p);
+		return node.getParent();
+	}
+	
+	/**returns the position of p's left child (or null if no child exists)*/
+	public Position<E> left(Position<E> p) throws IllegalArgumentException {
+		Node<E> node = validate(p);
+		return node.getLeft();
+	}
+	
+	/**returns the position of p's right child (or null if no child exists)*/
+	public Position<E> right(Position<E> p) throws IllegalArgumentException {
+		Node<E> node=validate(p);
+		return node.getRight();
+	}
+	
+	//update methods supported
+	/**places element e at the root of an empty tree and returns its new Position */
+	public Position<E> addRoot(E e) throws IllegalStateException {
+		if (!isEmpty()){throw new IllegalStateException("tree is not empty");}
+		root=createNode(e, null, null, null);
+		size=1;
+		return root;
+	}
+	
+	/**creates a new left child of Position P storing element e, returns its position*/
+	public Position<E> addLeft(Position<E> p, E e) throws IllegalArgumentException{
+		Node<E> parent=validate(p);
+		if(parent.getLeft()!=null){
+			throw new IllegalArgumentException("p already has a left child");
+		}
+		Node<E> child=createNode(e, parent, null, null);
+		parent.setLeft(child);
+		size++;
+		return child;
+	}
+	
+	public Position<E> addRight(Position<E> p, E e)throws IllegalArgumentException{
+		Node<E> parent=validate(p);
+		if(parent.getRight()!=null){
+			throw new IllegalArgumentException("p already has a right child");
+		}
+		Node<E> child=createNode(e, parent, null, null);
+		parent.setRight(child);
+		size++;
+		return child;
+	}
+	
+	/**replaces the element at position p with e and returns the replaced element*/
+	public E set(Position<E> p, E e) throws IllegalArgumentException{
+		Node<E> node=validate(p);
+		E temp=node.getElement();
+		node.setElement(e);
+		return temp;
+	}
+	
+	/**attaches trees t1 and t2 as left and right subtrees of external p.*/
+	public void attach(Position<E> p, LinkedBinaryTree<E> t1, LinkedBinaryTree<E> t2)throws IllegalArgumentException{
+		Node<E> node=validate(p);
+		if(isInternal(p)) throw new IllegalArgumentException("P must be a leaf");
+		size+=t1.size()+t2.size();
+		//set t1 as left node
+		if(!t1.isEmpty()){
+			t1.root.setParent(node);
+			node.setLeft(t1.root);
+			t1.root=null;
+			t1.size=0;
+		}
+		
+		//set t2 as right node
+		if(!t2.isEmpty()){
+			t2.root.setParent(node);
+			node.setRight(t2.root);
+			t2.root=null;
+			t2.size=0;
+		}
+	}
+		/**removes the node at Position p and replaces it with its child. only works if p has 1 or 0 children*/
+		public E remove(Position<E> p)throws IllegalArgumentException{
+			Node<E> node=validate(p);
+			if(numChildren(p)==2){throw new IllegalArgumentException("p has two children");}
+			Node<E> child=(node.getLeft()!=null?node.getLeft():node.getRight());
+			//childs grandparent becomes its parent
+			if(child!=null){child.setParent(node.getParent());}
+			
+			//child becomes root;
+			if(node==root){root=child;}
+			//child is not root, set child as child of parent
+			else{
+				Node<E> parent = node.getParent();
+				if(node==parent.getLeft()){parent.setLeft(child);}
+				else{parent.setRight(child);}
+			}
+			size--;
+			E temp=node.getElement();
+			//help java GC. sometimes I think it would be easier to do manual GC than have to baby along an auto GC.
+			node.setElement(null);
+			node.setLeft(null);
+			node.setRight(null);
+			//for some reason we set this to parent itself, instead of setting to null and sending to GC.
+			node.setParent(node);
+			return temp;
+		}
+}

Lab108-VenbergGE/src/PrevAssignmentClasses/LinkedQueue.java

@@ -0,0 +1,21 @@
+/*
+ * Data Structures & Algorithms 6th Edition 
+ * Goodrich, Tamassia, Goldwasser
+ * Code Fragment 6.11
+ * 
+ * An implementation of the LinkedQueue class
+ * */
+
+/**
+ *
+ * @author Gabriel Venberg
+ */
+public class LinkedQueue<E> implements Queue<E>{
+        private SinglyLinkedList<E> list = new SinglyLinkedList(); //an empty list
+        public LinkedQueue(){} //new queue relies on initaly empty list
+        public int size(){return list.size();}
+        public boolean isEmpty(){return list.isEmpty();}
+        public void enqueue(E element){list.addLast(element);}
+        public E first(){return list.first();}
+        public E dequeue(){return list.removeFirst();}
+}

Lab108-VenbergGE/src/PrevAssignmentClasses/Position.java

@@ -0,0 +1,21 @@
+/*
+ * Data Structures & Algorithms 6th Edition 
+ * Goodrich, Tamassia, Goldwasser
+ * Code Fragment 7.7
+ * 
+ * An implementation of the position interface
+ */
+
+/**
+ *
+ * @author Gabriel Venberg
+ */
+public interface Position<E> {
+    /**
+     * Returns the element stored at this position
+     * 
+     * @return the stored element
+     * @throws IllegalStateException if position no longer valid.
+     */
+    E getElement() throws IllegalStateException;
+}

Lab108-VenbergGE/src/PrevAssignmentClasses/PositionalList.java

@@ -0,0 +1,50 @@
+/*
+ * Data Structures & Algorithms 6th Edition 
+ * Goodrich, Tamassia, Goldwasser
+ * Code Fragment 7.8
+ * 
+ * An implementation of the positionalList interface
+ */
+
+/**
+ *
+ * @author Gabriel Venberg
+ */
+public interface PositionalList<E> {
+    
+    /** returns the number of elements in the list*/
+    int size();
+    
+    /**tests whether the list is empty*/
+    boolean isEmpty();
+    
+    /**returns the first position in the list (or null if empty)*/
+    Position<E> first();
+    
+    /**returns the last position in the list (or null if empty)*/
+    Position<E> last();
+    
+    /**returns the position immediately before position p (or null, if p is first)*/
+    Position<E> before(Position<E> p) throws IllegalArgumentException;
+    
+    /**returns the position immediately after position p (or null, if p is last)*/
+    Position<E> after(Position<E> p) throws IllegalArgumentException;
+    
+    /**inserts element e at the front of the list and returns its new position*/
+    Position<E> addFirst(E e);
+    
+    /**inserts element e at the back of the list and returns its new position*/
+    Position<E> addLast(E e);
+    
+    /**inserts element e immediately before position p and returns its new position*/
+    Position<E> addBefore(Position<E> p, E e) throws IllegalArgumentException;
+    
+    /**inserts element e immediately after Position p and returns its new position*/
+    Position<E> addAfter(Position<E> p, E e) throws IllegalArgumentException;
+    
+    /**replaces the element stored at position p and returns the replaced element*/
+    E set(Position<E> p, E e) throws IllegalArgumentException;
+    
+    /**removes the element stored at position p and returns it (invalidating p)*/
+    E remove(Position<E> p) throws IllegalArgumentException;
+}

Lab108-VenbergGE/src/PrevAssignmentClasses/Queue.java

@@ -0,0 +1,28 @@
+/**
+ * Data Structures & Algorithms 6th Edition 
+ * Goodrich, Tamassia, Goldwasser
+ * Code Fragment 6.9
+ * 
+ * An implementation of the Queue interface
+ * */
+
+/**
+ *
+ * @author Gabriel Venberg
+ */
+public interface Queue<E> {
+    /** returns the number of elements in the queue*/
+    int size();
+    
+    /** tests whether the queue is empty*/
+    boolean isEmpty();
+    
+    /**inserts an element at the rear of the queue*/
+    void enqueue(E e);
+    
+    /**returns, but does not remove, the first element of the queue (null if empty). */
+    E first();
+    
+    /** removes and returns the first element of the queue (null if empty)*/
+    E dequeue();
+}

Lab108-VenbergGE/src/PrevAssignmentClasses/SinglyLinkedList.java

@@ -0,0 +1,78 @@
+/**
+ *SinglyLinkedListClass
+ * Code Fragments 3.14, 3.15
+ * from
+ * Data Structures & Algorithms, 6th edition
+ * by Michael T. Goodrich, Roberto Tamassia & Michael H. Goldwasser
+ * Wiley 2014
+ * Transcribed by
+ * @author Gabe Venberg
+ */
+public class SinglyLinkedList<E> {
+    
+    private static class Node<E> {
+        private E element; //refrence to element stored at this node
+        private Node<E> next; //refrence to subsequent node of list
+        
+        public Node(E e, Node<E> n){
+            element = e;
+            next = n;
+        }
+        
+        public E getElement() {return element;}
+        
+        public Node<E> getNext() {return next;}
+        
+        public void setNext(Node<E> n) {next = n;}
+    }
+    
+    //instance variables of SinglyLinkedList
+    private Node<E> head = null;//head node of list
+    private Node<E> tail = null;//last node of list
+    private int size = 0;//number of nodes in list
+    
+    public SinglyLinkedList(){}//constructs an initaly empty list
+    
+    //access methods
+    public int size() {return size;}
+    
+    public boolean isEmpty() {return size == 0;}
+    
+    public E first(){//returns but does not remove the first element
+        if (size == 0) {return null;} //special case
+        return head.getElement();
+    }
+    
+    public E last(){//returns but does not remove last elemnt
+        if (size ==0) {return null;}//special case
+        return tail.getElement();
+    }
+    
+    //update methods
+    public void addFirst(E e){//adds element e to the front of the list
+        head = new Node<>(e, head);//create and link a new node
+        if (size == 0) {tail = head;}//special case, head becomes tail also
+        size++;
+    }
+    
+    public void addLast(E e){//adds element to end of list
+        Node<E> newest = new Node<>(e, null);//create and link a new node
+        if(size == 0){//special case, previously empty list
+            head = newest;
+        }
+        else{
+            tail.setNext(newest);//new node after existing tail
+        }
+        tail = newest;//new node becomes tail
+        size++;
+    }
+    
+    public E removeFirst(){//removes and returns the first element
+        if(size == 0){return null;}//nothing to remove
+        E answer = head.getElement();
+        head = head.getNext();//will become null if list had only one node.
+        size--;
+        if(size==0){tail = null;}// special case as list is now empty
+        return answer;
+    }
+}

Lab108-VenbergGE/src/PrevAssignmentClasses/Stack.java

@@ -0,0 +1,46 @@
+/**
+ * Data Structures & Algorithms 6th Edition 
+ * Goodrich, Tamassia, Goldwasser
+ * Code Fragment 6.1
+ * 
+ * An implementation of the stack interface
+ * */
+
+/**
+ * A collection of objects that are inserted and removed according to a last-in
+ * first-out principle. Although similar in purpose, this interface differs from
+ * java.util.stack.
+ * @author Gabriel Venberg
+ */
+public interface Stack<E> {
+    
+    /**
+     * returns the number of elements in the stack
+     * @return number of elements in the stack.
+     */
+    int size();
+    
+    /**
+     * tests whether the stack is empty.
+     * @return true if stack is empty, false otherwise.
+     */
+    boolean isEmpty();
+    
+    /**
+     * inserts an element at the top of the stack.
+     * @param e the element to be inserted.
+     */
+    void push(E e);
+    
+    /**
+     * returns, but does not remove, the top element of the stack.
+     * @return top element of the stack or null if empty.
+     */
+    E top();
+    
+    /**
+     * removes and returns the top element from the stack.
+     * @return element removed or null if empty.
+     */
+    E pop();
+}

Lab108-VenbergGE/src/PrevAssignmentClasses/Tree.java

@@ -0,0 +1,29 @@
+
+import java.util.Iterator;
+
+/*
+ * Data Structures & Algorithms 6th Edition 
+ * Goodrich, Tamassia, Goldwasser
+ * Code Fragment 8.1
+ * 
+ * An implementation of the tree interface
+ */
+
+
+/**
+ * An interface for a tree where nodes can have an arbitrary number of children.
+ * @author Gabriel Venberg
+ */
+public interface Tree<E> extends Iterable<E>{
+	Position <E> root();
+	Position<E> parent(Position<E> p) throws IllegalArgumentException;
+	Iterable<Position<E>> children(Position<E> p) throws IllegalArgumentException;
+	int numChildren(Position<E> p) throws IllegalArgumentException;
+	boolean isInternal(Position<E> p) throws IllegalArgumentException;
+	boolean isExternal(Position<E> p) throws IllegalArgumentException;
+	boolean isRoot(Position<E> p) throws IllegalArgumentException;
+	int size();
+	boolean isEmpty();
+	Iterator<E> iterator();
+	Iterable<Position<E>> positions();
+}