.gitea/workflows/gradle_build.yml

@@ -0,0 +1,24 @@
+name: sample gradle build and test
+run-name: Build started by $ {{gitea.actor }}
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out repository code
+        uses: actions/checkout@v4
+      - name: JDK setup
+        uses: actions/setup-java@v4
+        with:
+          distribution: 'zulu'
+          java-version: '21'
+      - name: Validate Gradle Wrapper
+        uses: gradle/actions/wrapper-validation@v3
+      - name: Gradle build
+        run: ./gradlew build -i
+

.idea/vcs.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="" vcs="Git" />
+  </component>
+</project>

clients/src/main/java/com/hithomelabs/clients/ArrayQueueClient.java

@@ -0,0 +1,20 @@
+package com.hithomelabs.clients;
+
+import com.hithomelabs.princeton1.module4.ArrayQueue;
+import com.hithomelabs.princeton1.module4.Queue;
+
+public class ArrayQueueClient {
+    public static void main(String[] args) {
+        Queue<Integer> queue = new ArrayQueue<Integer>();
+        for(int i = 0; i < 21; i++){
+            queue.enqueue(i);
+        }
+        for(int i = 0; i < 13; i++){
+            System.out.println(queue.dequeue());
+        }
+
+        // Using object s, as stack is generic but every java Object has implementation of toString()
+        for (Object s : queue)
+            System.out.println(s);
+        }
+    }

clients/src/main/java/com/hithomelabs/clients/ArrayStackClient.java

@@ -0,0 +1,19 @@
+package com.hithomelabs.clients;
+
+import com.hithomelabs.princeton1.module4.ArrayStack;
+import com.hithomelabs.princeton1.module4.Stack;
+
+public class ArrayStackClient {
+    public static void main(String[] args) {
+        Stack<Integer> stack = new ArrayStack<Integer>();
+        for(int i = 0; i < 21; i++){
+            stack.push(i);
+        }
+        // Using object s, as stack is generic but every java Object has implementation of toString()
+        for (Object s : stack)
+            System.out.println(s);
+        while(!stack.isEmpty()){
+            System.out.println(stack.pop());
+        }
+    }
+}

clients/src/main/java/com/hithomelabs/clients/LinkedQueueClient.java

@@ -0,0 +1,20 @@
+package com.hithomelabs.clients;
+
+import com.hithomelabs.princeton1.module4.LinkedQueue;
+import com.hithomelabs.princeton1.module4.Queue;
+
+public class LinkedQueueClient {
+    public static void main(String[] args) {
+        Queue<Integer> queue = new LinkedQueue<Integer>();
+        for(int i = 0; i < 21; i++){
+            queue.enqueue(i);
+        }
+        for(int i = 0; i < 13; i++){
+            System.out.println(queue.dequeue());
+        }
+
+        // Using object s, as stack is generic but every java Object has implementation of toString()
+        for (Object s : queue)
+            System.out.println(s);
+        }
+    }

clients/src/main/java/com/hithomelabs/clients/LinkedStackClient.java

@@ -4,7 +4,7 @@ package com.hithomelabs.clients;
 import com.hithomelabs.princeton1.module4.LinkedStack;
 import com.hithomelabs.princeton1.module4.Stack;
 
-public class Main {
+public class LinkedStackClient {
     public static void main(String[] args) {
         Stack<String> stack = new LinkedStack<String>();
         stack.push("hello");

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

@@ -0,0 +1,103 @@
+package com.hithomelabs.princeton1.module4;
+
+import javax.annotation.Nonnull;
+import java.util.Iterator;
+
+public class ArrayQueue<E> extends Queue<E>{
+
+    // 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 size == 0;
+    }
+
+    @Override
+    public E dequeue() {
+        if(isEmpty())
+            return null;
+        else{
+            E element = arr[head];
+            // Garbage collection
+            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(E element) {
+        // We plan capacity expansion if needed
+        if (size == capacity){
+            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 size;
+    }
+
+    @Override
+    @Nonnull
+    public Iterator<E> iterator() {
+        return new Iterator<E>() {
+            int counter = size;
+            int pointer = head;
+            @Override
+            public boolean hasNext() {
+                return counter != 0;
+            }
+
+            @Override
+            public E next() {
+                E element = arr[pointer];
+                pointer = (pointer + 1)% capacity;
+                --counter;
+                return element;
+            }
+        };
+    }
+}

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

@@ -0,0 +1,98 @@
+package com.hithomelabs.princeton1.module4;
+import javax.annotation.Nonnull;
+import java.util.Iterator;
+
+// Concrete implementation of stack using arrays
+// Creating a generic stack of type E
+public class ArrayStack<E> extends Stack<E> {
+
+    // Capacity and size are two variables, capacity determines total capacity of array, capacity defaults at 10
+    // Everytime size == capacity, capacity = 2 * 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 parametrised constructor with default initial capacity 10
+    public ArrayStack(){
+        this(DEFAULT_CAPACITY);
+    }
+
+    @Override
+    public boolean isEmpty() {
+        return size == 0;
+    }
+
+    private void changeCapacity(int newCapacity){
+        E[] resizedArr = (E[]) new Object[newCapacity];
+        for (int i = 0; i < size; i++)
+            resizedArr[i] = arr[i];
+        arr = resizedArr;
+    }
+
+    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 E pop() {
+        if (isEmpty())
+            return null;
+        else{
+            E e = arr[--size];
+            arr[size] = null;
+            checkResize();
+            return e;
+        }
+    }
+
+    private void checkResize() {
+        if (size < capacity / 4 && capacity >= 40){
+            capacity = capacity / 2;
+            changeCapacity(capacity);
+        }
+    }
+
+    @Override
+    public int size() {
+        return size;
+    }
+
+    @Override
+    @Nonnull
+    public Iterator<E> iterator() {
+        return new Iterator<E>() {
+
+            int current = 0;
+
+            @Override
+            public boolean hasNext() {
+                return current != size;
+            }
+
+            @Override
+            public E next() {
+                E element = arr[current];
+                current = current + 1;
+                return element;
+            }
+        };
+    }
+}

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

@@ -0,0 +1,74 @@
+package com.hithomelabs.princeton1.module4;
+
+import javax.annotation.Nonnull;
+import java.util.Iterator;
+
+public class LinkedQueue<E> extends Queue<E>{
+
+    Node head;
+    Node tail;
+    int size;
+
+    private class Node{
+        E value;
+        Node next;
+
+        Node(E value){
+            this.value = value;
+        }
+    }
+
+    @Override
+    public boolean isEmpty() {
+        return size==0;
+    }
+
+    @Override
+    public E dequeue() {
+        if(isEmpty())
+            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(E element) {
+        Node newNode = new Node(element);
+        if(isEmpty())
+            head = newNode;
+        else
+            tail.next = newNode;
+        tail = newNode;
+        ++size;
+    }
+
+    @Override
+    public int size() {
+        return size;
+    }
+
+    @Override
+    @Nonnull
+    public Iterator<E> iterator() {
+        return new Iterator<E>() {
+            Node current = head;
+            @Override
+            public boolean hasNext() {
+                return current != tail;
+            }
+
+            @Override
+            public E next() {
+                E element = current.value;
+                current = current.next;
+                return element;
+            }
+        };
+    }
+}

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

@@ -0,0 +1,10 @@
+package com.hithomelabs.princeton1.module4;
+
+public abstract class Queue<E> implements Iterable<E> {
+
+    public abstract boolean isEmpty();
+    public abstract E dequeue();
+    public abstract void enqueue(E element);
+    public abstract int size();
+}
+