.idea/.name

@@ -1 +0,0 @@
-Pricenton1

.idea/Princeton1.iml

@@ -1,9 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<module type="JAVA_MODULE" version="4">
-  <component name="NewModuleRootManager" inherit-compiler-output="true">
-    <exclude-output />
-    <content url="file://$MODULE_DIR$" />
-    <orderEntry type="inheritedJdk" />
-    <orderEntry type="sourceFolder" forTests="false" />
-  </component>
-</module>

.idea/gradle.xml

@@ -4,8 +4,6 @@
   <component name="GradleSettings">
     <option name="linkedExternalProjectsSettings">
       <GradleProjectSettings>
-        <option name="delegatedBuild" value="false" />
-        <option name="testRunner" value="PLATFORM" />
         <option name="externalProjectPath" value="$PROJECT_DIR$" />
         <option name="modules">
           <set>
@@ -16,7 +14,6 @@
             <option value="$PROJECT_DIR$/module5" />
             <option value="$PROJECT_DIR$/module6" />
             <option value="$PROJECT_DIR$/module7" />
-            <option value="$PROJECT_DIR$/module8" />
           </set>
         </option>
       </GradleProjectSettings>

.idea/modules.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ProjectModuleManager">
+    <modules>
+      <module fileurl="file://$PROJECT_DIR$/.idea/modules/module4/Pricenton1.module4.test.iml" filepath="$PROJECT_DIR$/.idea/modules/module4/Pricenton1.module4.test.iml" />
+    </modules>
+  </component>
+</project>

module4/src/main/java/com/hithomelabs/princeton1/module4/ArrayQueue.java

@@ -2,65 +2,102 @@ package com.hithomelabs.princeton1.module4;
 
 import java.util.Iterator;
 
-public class ArrayQueue<Item> extends Queue<Item> {
+import javax.annotation.Nonnull;
 
-    private int capacity=3;
+public class ArrayQueue<E> extends Queue<E>{
-    private Item[] arr = (Item[]) new Object[capacity];
+
-    private int head=0,tail=0;
+    // insertion from tail, removal from head
+    public static final int DEFAULT_CAPACITY = 10;
+    private int capacity;
+    private int tail;
+    private int head;
+    private int size;
+    private E[] arr;
+
+    public ArrayQueue(){
+        this(DEFAULT_CAPACITY);
+    }
+
+    public ArrayQueue(int capacity){
+        this.capacity = capacity;
+        arr = (E[]) new Object[this.capacity];
+        size = 0;
+    }
 
     @Override
     public boolean isEmpty() {
-        return (tail - head) == 0;
+        return size == 0;
-    }
-
-    private void resize(int newCapacity){
-        Item[] temp = arr;
-        arr = (Item[]) new Object[newCapacity];
-        int iNew=0,iOld=head;
-        while(iOld<tail){
-            arr[iNew]=temp[iOld];
-            iNew++;
-            iOld++;
-        }
-
-        capacity=newCapacity;
     }
 
     @Override
-    public Item dequeue() {
+    public E dequeue() {
         if(isEmpty())
             return null;
-        //        System.out.println(head+" "+arr[head]);
+        else{
-        Item element = arr[head++];
+            E element = arr[head];
-        if(size() < capacity/4)
+            // Garbage collection
-            resize(capacity/2);
+            arr[head] = null;
+            head = (head+1)%capacity;
+            size = size - 1;
+            if(capacity >= 40 && size < capacity/4){
+                capacity = capacity/2;
+                resize(capacity, capacity*2);
+            }
             return element;
         }
+    }
 
     @Override
-    public void enqueue(Item element) {
+    public void enqueue(E element) {
-        if(tail == capacity)
+        // We plan capacity expansion if needed
-            resize(capacity * 2);
+        if (size == capacity){
-        arr[tail++] = element;
+            capacity = capacity * 2;
+            resize(capacity, capacity/2);
+        }
+        arr[tail] = element;
+        tail = (tail + 1) % capacity;
+        ++size;
+    }
+
+    // When resize takes place always the original array is full, so copy the complete array as is
+    private void resize(int capacity, int oldCapacity) {
+        E[] resizedArr = (E[]) new Object[capacity];
+        for(int i = 0; i < size; i++) {
+            resizedArr[i] = arr[head];
+            // halving because capacity has now doubled
+            arr[head] = null;
+            head = (head + 1) % oldCapacity;
+        }
+        arr = resizedArr;
+        // When resizing takes place, we bring the head to 0 and the tail to size
+        // tail is where new inserts will be made and head will be where elements will be removed
+        tail = size;
+        head = 0;
+
     }
 
     @Override
     public int size() {
-        return (tail - head);
+        return size;
     }
 
     @Override
-    public Iterator<Item> iterator() {
+    @Nonnull
-        return new Iterator<Item>() {
+    public Iterator<E> iterator() {
-            int current = head;
+        return new Iterator<E>() {
+            int counter = size;
+            int pointer = head;
             @Override
             public boolean hasNext() {
-                return current != tail;
+                return counter != 0;
             }
 
             @Override
-            public Item next() {
+            public E next() {
-                return arr[current++];
+                E element = arr[pointer];
+                pointer = (pointer + 1)% capacity;
+                --counter;
+                return element;
             }
         };
     }

module4/src/main/java/com/hithomelabs/princeton1/module4/ArrayStack.java

@@ -1,109 +1,98 @@
 package com.hithomelabs.princeton1.module4;
-
 import java.util.Iterator;
+import javax.annotation.Nonnull;
 
-public class ArrayStack<Item> extends Stack<Item>{
+// Concrete implementation of stack using arrays
+// Creating a generic stack of type E
+public class ArrayStack<E> extends Stack<E> {
 
-    private int capacity=3;
+    // Capacity and size are two variables, capacity determines total capacity of array, capacity defaults at 10
-    private int top=0;
+    // every time size == capacity, capacity = 2 * capacity
-    private Item[] arr = (Item[]) new Object[capacity];
+    private static final int DEFAULT_CAPACITY = 10;
+    private int capacity;
+    private int size;
+    private E[] arr;
 
+    public ArrayStack(int capacity){
+        this.capacity = capacity;
+        arr = (E[]) new Object[this.capacity];
+    }
+
+    // Constructor chaining, default constructor will call parametrized constructor with default initial capacity 10
+    public ArrayStack(){
+        this(DEFAULT_CAPACITY);
+    }
 
     @Override
     public boolean isEmpty() {
-        return top == 0;
+        return size == 0;
     }
 
-    private void resize(int newCapacity){
+    private void changeCapacity(int newCapacity){
-        Item[] temp = arr;
+        E[] resizedArr = (E[]) new Object[newCapacity];
-        arr = (Item[]) new Object[newCapacity];
+        for (int i = 0; i < size; i++)
-
+            resizedArr[i] = arr[i];
-        for(int i=0; i<top; i++){
+        arr = resizedArr;
-            arr[i]=temp[i];
     }
-        capacity=newCapacity;
+
-//        System.out.println("New Capacity: "+capacity);
+    private void incrementSize(){
+        if (size == capacity){
+            capacity = 2 * capacity;
+            changeCapacity(capacity);
+        }
+    }
+
+    // Push always happens at the end of the stack
+    // Say the size of the stack is 1, new element gets inserted  at 1
+    @Override
+    public void push(E element) {
+        // Lazy approach, we assume size to always be lesser than capacity
+        incrementSize();
+        arr[size++] = element;
     }
 
     @Override
-    public void push(Item element) {
+    public E pop() {
-        if(top == capacity)
+        if (isEmpty())
-            resize(capacity * 2);
-        arr[top++] = element;
-    }
-
-    @Override
-    public Item pop() {
-
-        //System.out.println(top);
-
-        if(top == 0)
-            //throw new java.util.NoSuchElementException();
             return null;
+        else{
+            E e = arr[--size];
+            arr[size] = null;
+            checkResize();
+            return e;
+        }
+    }
 
-        Item element = arr[--top];
+    private void checkResize() {
-        arr[top] = null;
+        if (size < capacity / 4 && capacity >= 20){
-
+            capacity = capacity / 2;
-        if(top < capacity/4)
+            changeCapacity(capacity);
-            resize(capacity/2);
+        }
-        return element;
     }
 
     @Override
     public int size() {
-        return top;
+        return size;
     }
 
     @Override
-    public Iterator<Item> iterator() {
+    @Nonnull
-        return new Iterator<Item>() {
+    public Iterator<E> iterator() {
-            private int current=0;
+        return new Iterator<E>() {
+
+            int current = 0;
+
             @Override
             public boolean hasNext() {
-                return current<top;
+                return current != size;
             }
 
             @Override
-            public Item next() {
+            public E next() {
-                return arr[current++];
+                E element = arr[current];
+                current = current + 1;
+                return element;
             }
         };
     }
-
-    public static void main(String[] args){
-        Stack<Integer> s = new ArrayStack<>();
-
-        try{
-            s.push(0);
-            s.push(1);
-            s.push(2);
-            s.push(3);
-            s.push(4);
-            s.push(5);
-            s.push(6);
-            s.push(7);
-
-            for(Integer i: s)
-                System.out.println(i);
-
-            s.pop();
-            s.pop();
-            s.pop();
-            s.pop();
-            s.pop();
-            s.pop();
-            s.pop();
-            s.pop();
-//            s.pop();
-
-            for(Integer i: s)
-                System.out.println(i);
-
-        } catch (java.util.NoSuchElementException e) {
-            System.out.println("Cannot pop an empty stack");
-        }
-
-
-
-    }
 }

module4/src/main/java/com/hithomelabs/princeton1/module4/Deque.java

@@ -1,136 +0,0 @@
-package com.hithomelabs.princeton1.module4;
-
-
-import java.util.Iterator;
-
-public class Deque<Item> implements Iterable<Item> {
-
-    private Node head;
-    private Node tail;
-    private int capacity;
-
-    private class Node{
-        Item value;
-        Node next;
-    }
-
-    public Deque(){
-        this.head = null;
-        this.tail = null;
-        this.capacity = 0;
-    }
-
-    public boolean isEmpty(){
-        return this.capacity == 0;
-    }
-
-    public int size(){
-        return this.capacity;
-    }
-
-
-    public void addFirst(Item item){
-            Node temp=this.head;
-            this.head=new Node();
-            this.head.value = item;
-            this.head.next = temp;
-//            System.out.println(this.isEmpty());
-            if(this.isEmpty())
-                this.tail=this.head;
-            this.capacity++;
-    }
-
-    public void addLast(Item item){
-        Node temp = new Node();
-        temp.value = item;
-        System.out.println(this.isEmpty());
-        if(!this.isEmpty()) {
-            this.tail.next = temp;
-            this.tail = this.tail.next;
-        }
-        else{
-            this.head = temp;
-            this.tail = temp;
-        }
-        this.capacity++;
-    }
-
-    public Item removeFirst(){
-        Item item = this.head.value;
-        this.head=this.head.next;
-        this.capacity--;
-        return item;
-    }
-
-    public Item removeLast(){
-        Item item = this.tail.value;
-        Node temp = this.head;
-
-        if(capacity <= 1){
-            this.tail=null;
-            this.head=null;
-            return item;
-        }
-
-
-        while(temp.next.next != null){
-            temp=temp.next;
-        }
-
-        this.tail=temp;
-        this.tail.next=null;
-        this.capacity--;
-        return item;
-    }
-
-    @Override
-    public Iterator<Item> iterator() {
-
-        return new Iterator<Item>() {
-            private Node current=head;
-            @Override
-            public boolean hasNext() {
-                return this.current != null;
-            }
-
-            @Override
-            public Item next() {
-                Item item = this.current.value;
-                this.current=this.current.next;
-                return item;
-            }
-        };
-    }
-
-    public static void main(String[] args){
-        Deque<String> deque = new Deque<String>();
-
-        deque.addLast("qwe");
-        deque.addFirst("asd");
-        deque.addLast("zxc");
-
-        for(String s: deque){
-            System.out.println(s);
-        }
-
-        deque.addLast("qwess");
-
-        System.out.println();
-
-        for(String s: deque){
-            System.out.println(s);
-        }
-
-        deque.removeFirst();
-        deque.removeLast();
-        deque.removeFirst();
-        deque.removeLast();
-
-        System.out.println();
-
-        for(String s: deque){
-            System.out.println(s);
-        }
-
-    }
-}

module4/src/main/java/com/hithomelabs/princeton1/module4/LinkedQueue.java

@@ -1,14 +1,21 @@
 package com.hithomelabs.princeton1.module4;
 
+import javax.annotation.Nonnull;
 import java.util.Iterator;
 
-public class LinkedQueue<Item> extends Queue<Item>{
+public class LinkedQueue<E> extends Queue<E>{
-    private Node head = null, tail = null;
+
-    private int size = 0;
+    Node head;
+    Node tail;
+    int size;
 
     private class Node{
-        Item value;
+        E value;
         Node next;
+
+        Node(E value){
+            this.value = value;
+        }
     }
 
     @Override
@@ -17,34 +24,28 @@ public class LinkedQueue<Item> extends Queue<Item>{
     }
 
     @Override
-    public Item dequeue() {
+    public E dequeue() {
-        if(size == 0)
-//            throw new java.util.NoSuchElementException();
-            return null;
-
-        Item element = head.value;
-        head = head.next;
-        size--;
         if(isEmpty())
-            tail=head;
+            return null;
+        E element = head.value;
+        // Only a single element is present
+        if (head == tail){
+            tail = null;
+        }
+        head = head.next;
+        --size;
         return element;
     }
 
     @Override
-    public void enqueue(Item element) {
+    public void enqueue(E element) {
-        Node newNode = new Node();
+        Node newNode = new Node(element);
-        newNode.value = element;
+        if(isEmpty())
-        newNode.next = null;
+            head = newNode;
-        if(isEmpty()){
+        else
-            tail=newNode;
-            head=tail;
-        }
-        else{
             tail.next = newNode;
-            tail = tail.next;
+        tail = newNode;
-        }
+        ++size;
-        size++;
-
     }
 
     @Override
@@ -53,8 +54,9 @@ public class LinkedQueue<Item> extends Queue<Item>{
     }
 
     @Override
-    public Iterator<Item> iterator() {
+    @Nonnull
-        return new Iterator<Item>() {
+    public Iterator<E> iterator() {
+        return new Iterator<E>() {
             Node current = head;
             @Override
             public boolean hasNext() {
@@ -62,42 +64,11 @@ public class LinkedQueue<Item> extends Queue<Item>{
             }
 
             @Override
-            public Item next() {
+            public E next() {
-                Item element = current.value;
+                E element = current.value;
                 current = current.next;
                 return element;
             }
         };
-
-    }
-
-    public static void main(String[] args){
-        Queue<Integer> q = new LinkedQueue<>();
-
-        try{
-            System.out.println("Queue empty?: " + q.isEmpty());
-            q.enqueue(1);
-            q.enqueue(2);
-            q.enqueue(3);
-            q.enqueue(4);
-
-            for(int value: q)
-                System.out.println(value);
-
-            System.out.println("Queue empty?: " + q.isEmpty());
-            System.out.println("Queue Size?: " + q.size());
-
-            q.dequeue();
-            q.dequeue();
-//            q.dequeue();
-//            q.dequeue();
-//            q.dequeue();
-
-            for(int value: q)
-                System.out.println(value);
-
-        } catch (java.util.NoSuchElementException e) {
-            System.out.println("Cannot dequeue empty queue");
-        }
     }
 }

module4/src/main/java/com/hithomelabs/princeton1/module4/LinkedStack.java

@@ -1,86 +1,72 @@
 package com.hithomelabs.princeton1.module4;
-
 import java.util.Iterator;
 
-public class LinkedStack<Item> extends Stack<Item> {
+// Creating a concrete linked Implementation of Stack
+public class LinkedStack<E> extends Stack<E>{
 
-    private Node top = null;
+    // No need for an explicit constructor as size will be initialized to 0 and root to null
-    private int size = 0;
+    private int size;
+    private Node first;
 
+    // By default instance variables are package private
     private class Node{
-        Item value;
+        E value;
         Node next;
     }
 
-
+    // Will return true if size is 0
     @Override
     public boolean isEmpty() {
-        return size == 0 ;
+        return (this.size == 0);
     }
 
+    // Adds an element to the start of a linked list
     @Override
-    public void push(Item element) {
+    public void push(E element) {
         Node newNode = new Node();
         newNode.value = element;
-        newNode.next = top;
+        newNode.next = first;
-        top = newNode;
+        first = newNode;
-//        System.out.println(top.value);
+        this.size = this.size + 1;
-        size++;
     }
 
     @Override
-    public Item pop() {
+    public E pop() {
-        if(size == 0){
+        if (this.isEmpty())
-            throw new java.util.NoSuchElementException();
+            return null;
+        else{
+            Node toBePopped = first;
+            first = first.next;
+            this.size = this.size - 1;
+            return toBePopped.value;
         }
-        Item element = top.value;
-        top=top.next;
-        size--;
-
-        return element;
     }
 
     @Override
     public int size() {
-        return size;
+        return this.size;
     }
 
     @Override
-    public Iterator<Item> iterator() {
+    public Iterator<E> iterator() {
-        return new Iterator<Item>() {
+        return new Iterator<E>() {
-            private Node current = top;
+
+            // Internal classes can access outer objects
+            Node current = first;
             @Override
             public boolean hasNext() {
                 return current != null;
             }
 
             @Override
-            public Item next() {
+            public E next() {
-                Item element = current.value;
+                E element = current.value;
                 current = current.next;
                 return element;
             }
         };
     }
 
-    public static void main(String[] args){
-        Stack <String> s = new LinkedStack<>();
 
-        try {
-            System.out.println("String empty?: " + s.isEmpty());
-//            s.pop();
-            s.push("12");
-            s.push("13");
-            s.pop();
-            s.push("14");
-            System.out.println("String empty?: " + s.isEmpty());
-            System.out.println("String size?: " + s.size());
 
-            for(String value: s){
-                System.out.print(value+" ");
-            }
-        } catch (Exception e) {
-            System.out.println("Cannot pop an empty stack");
-        }
-    }
 }