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

@@ -6,23 +6,11 @@ import javax.annotation.Nonnull;
 
 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 E[] queueArray = (E[]) new Object[5];
+    private int startPtr;
+    private int endPtr;
     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;
-    }
+    private int queueArrayLength = queueArray.length;
 
     @Override
     public boolean isEmpty() {
@@ -31,49 +19,25 @@ public class ArrayQueue<E> extends Queue<E>{
 
     @Override
     public E dequeue() {
-        if(isEmpty())
+        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;
         }
+        E currentValue = queueArray[startPtr % queueArrayLength];
+        queueArray[startPtr++ % queueArrayLength] = null;
+        size--;
+        if(size() < queueArrayLength/4){
+            changeArraySize(queueArrayLength/2);
+        }
+        return currentValue;
     }
 
     @Override
     public void enqueue(E element) {
-        // We plan capacity expansion if needed
-        if (size == capacity){
-            capacity = capacity * 2;
-            resize(capacity, capacity/2);
+        queueArray[endPtr++ % queueArrayLength] = element;
+        size++;
+        if(size == queueArrayLength){
+            changeArraySize(queueArrayLength*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
@@ -81,24 +45,37 @@ public class ArrayQueue<E> extends Queue<E>{
         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;
-            }
+    private void changeArraySize(int targetSize){
+        E[] tempArray = queueArray;
+        int oldArraySize = tempArray.length;
+        queueArray = (E[]) new Object[targetSize];
+        int j = 0;
 
-            @Override
-            public E next() {
-                E element = arr[pointer];
-                pointer = (pointer + 1)% capacity;
-                --counter;
-                return element;
-            }
-        };
+        for(int i=0; i<size; i++)
+            queueArray[j++]=tempArray[(startPtr+i)%oldArraySize];
+        endPtr = size();
+        startPtr = 0;
+        queueArrayLength = queueArray.length;
+    }
+
+    @Nonnull
+    @Override
+    public Iterator<E> iterator() {
+        return new QueueArrayIterator();
+    }
+
+    private class QueueArrayIterator implements Iterator<E>{
+
+        private int iteratorIndex = startPtr;
+
+        @Override
+        public boolean hasNext() {
+            return iteratorIndex % queueArrayLength < endPtr % queueArrayLength;
+        }
+
+        @Override
+        public E next() {
+            return queueArray[iteratorIndex++ % queueArrayLength];
+        }
     }
 }

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

@@ -6,93 +6,68 @@ import javax.annotation.Nonnull;
 // 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
-    // every time 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 parametrized constructor with default initial capacity 10
-    public ArrayStack(){
-        this(DEFAULT_CAPACITY);
-    }
+    E[] stackArray = (E[]) new Object[1];
+    private int index = 0;
+    private int arrayLength = stackArray.length;
 
     @Override
     public boolean isEmpty() {
-        return size == 0;
+        return index == 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;
+        if(index == arrayLength){
+            changeArraySize(arrayLength*2);
+        }
+        stackArray[index] = element;
+        index++;
     }
 
     @Override
     public E pop() {
-        if (isEmpty())
+        if(index == 0){
             return null;
-        else{
-            E e = arr[--size];
-            arr[size] = null;
-            checkResize();
-            return e;
         }
-    }
-
-    private void checkResize() {
-        if (size < capacity / 4 && capacity >= 20){
-            capacity = capacity / 2;
-            changeCapacity(capacity);
+        index--;
+        if(index < arrayLength/4){
+            changeArraySize(arrayLength/2);
         }
+        E temp = stackArray[index];
+        stackArray[index] = null;
+        return temp;
     }
 
     @Override
     public int size() {
-        return size;
+        return index;
     }
 
-    @Override
     @Nonnull
+    @Override
     public Iterator<E> iterator() {
-        return new Iterator<E>() {
+        return new StackIterator();
+    }
 
-            int current = 0;
+    private void changeArraySize(int intendedSize){
+        E[] tempArray = stackArray;
+        int oldArraySize = stackArray.length;
+        stackArray = (E[]) new Object[intendedSize];
+        arrayLength = stackArray.length;
+        System.arraycopy(tempArray, 0, stackArray, 0, Math.min(oldArraySize, arrayLength));
+    }
 
-            @Override
-            public boolean hasNext() {
-                return current != size;
-            }
+    private class StackIterator implements Iterator<E>{
+        private int iteratorIndex = 0;
 
-            @Override
-            public E next() {
-                E element = arr[current];
-                current = current + 1;
-                return element;
-            }
-        };
+        @Override
+        public boolean hasNext() {
+            return stackArray[iteratorIndex] != null;
+        }
+
+        @Override
+        public E next() {
+            return stackArray[iteratorIndex++];
+        }
     }
 }

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

@@ -5,70 +5,76 @@ import java.util.Iterator;
 
 public class LinkedQueue<E> extends Queue<E>{
 
-    Node head;
-    Node tail;
-    int size;
+    Node<E> start = null;
+    Node<E> end = null;
 
-    private class Node{
-        E value;
-        Node next;
+    static private class Node<E>{
+        E data;
+        Node<E> next;
 
-        Node(E value){
-            this.value = value;
+        private Node(E element){
+            data=element;
+            next=null;
         }
     }
 
     @Override
     public boolean isEmpty() {
-        return size==0;
+        return start == null;
     }
 
     @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;
+        E currentValue = start.data;
+        start = start.next;
+        if(isEmpty())
+            end = null;
+        return currentValue;
     }
 
     @Override
     public void enqueue(E element) {
-        Node newNode = new Node(element);
+        Node<E> new_node = new Node<E>(element);
         if(isEmpty())
-            head = newNode;
+            start = new_node;
         else
-            tail.next = newNode;
-        tail = newNode;
-        ++size;
+            end.next = new_node;
+        end = new_node;
     }
 
     @Override
     public int size() {
+        int size = 0;
+        Node<E> sizePtr = start;
+        while (sizePtr != null) {
+            sizePtr = sizePtr.next;
+            size++;
+        }
         return size;
     }
 
-    @Override
     @Nonnull
+    @Override
     public Iterator<E> iterator() {
-        return new Iterator<E>() {
-            Node current = head;
-            @Override
-            public boolean hasNext() {
-                return current != null;
-            }
+        return new LinkedQueueIterator();
+    }
 
-            @Override
-            public E next() {
-                E element = current.value;
-                current = current.next;
-                return element;
-            }
-        };
+    private class LinkedQueueIterator implements Iterator<E>{
+
+        Node<E> traversePtr = start;
+
+        @Override
+        public boolean hasNext() {
+            return traversePtr != null;
+        }
+
+        @Override
+        public E next() {
+            E currentValue = traversePtr.data;
+            traversePtr = traversePtr.next;
+            return currentValue;
+        }
     }
 }

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

@@ -1,72 +1,71 @@
 package com.hithomelabs.princeton1.module4;
+
+import javax.annotation.Nonnull;
 import java.util.Iterator;
 
 // Creating a concrete linked Implementation of Stack
 public class LinkedStack<E> extends Stack<E>{
 
-    // No need for an explicit constructor as size will be initialized to 0 and root to null
-    private int size;
-    private Node first;
+    static class Node<E>{
+        E data;
+        Node<E> next;
 
-    // By default instance variables are package private
-    private class Node{
-        E value;
-        Node next;
+        Node(E data) {
+            this.data = data;
+            this.next = null;
+        }
     }
 
-    // Will return true if size is 0
+    Node<E> head = null;
+    int stackLength = 0;
+
     @Override
     public boolean isEmpty() {
-        return (this.size == 0);
+        return head == null;
     }
 
-    // Adds an element to the start of a linked list
     @Override
     public void push(E element) {
-        Node newNode = new Node();
-        newNode.value = element;
-        newNode.next = first;
-        first = newNode;
-        this.size = this.size + 1;
+        Node<E> new_node = new Node<E>(element);
+        new_node.next = head;
+        head = new_node;
+        stackLength++;
     }
 
     @Override
     public E pop() {
-        if (this.isEmpty())
+        if(stackLength == 0)
             return null;
-        else{
-            Node toBePopped = first;
-            first = first.next;
-            this.size = this.size - 1;
-            return toBePopped.value;
-        }
+        E currentValue = head.data;
+        head = head.next;
+        return currentValue;
     }
 
     @Override
     public int size() {
-        return this.size;
+        return stackLength;
     }
 
+    @Nonnull
     @Override
     public Iterator<E> iterator() {
-        return new Iterator<E>() {
-
-            // Internal classes can access outer objects
-            Node current = first;
-            @Override
-            public boolean hasNext() {
-                return current != null;
-            }
-
-            @Override
-            public E next() {
-                E element = current.value;
-                current = current.next;
-                return element;
-            }
-        };
+        return new LinkedlistIterator();
     }
 
+    private class LinkedlistIterator implements Iterator<E>{
 
+        Node<E> iteratorPtr = head;
 
+        @Override
+        public boolean hasNext() {
+            return iteratorPtr.next != null;
+        }
+
+        @Override
+        public E next() {
+            E currentValue = iteratorPtr.data;
+            iteratorPtr = iteratorPtr.next;
+            return currentValue;
+        }
+    }
 }

module5/src/main/java/com/hithomelabs/princeton1/module5/AbstractCustomSorts.java

@@ -4,12 +4,14 @@ public abstract class AbstractCustomSorts<E> {
 
     public abstract void sort(E[] arr);
 
+    // TODO: Implement this method
     public void exch(E[] arr, int j, int i) {
         E temp = arr[i];
         arr[i] = arr[j];
         arr[j] = temp;
     }
 
+    // TODO: Implement this method
     public boolean less(Comparable<E> e1, E e2) {
         return e1.compareTo(e2) < 0;
     }

module5/src/main/java/com/hithomelabs/princeton1/module5/Insertion.java

@@ -1,23 +1,15 @@
 package com.hithomelabs.princeton1.module5;
 
 public class Insertion<E> extends AbstractCustomSorts<E> {
-
-    public void sort(E[] arr){
-        if (arr == null) return;
-        else{
-            int N = arr.length;
-            // * * swap arr[i] with each element greater to it's left
-            for (int i = 1; i < N; i++){
-                int j = i;
-                while(j >= 1 && less((Comparable<E>)arr[j], arr[j-1])){
-                    exch(arr, j, j-1);
-                    j = j-1;
-                }
+    @Override
+    public void sort(E[] arr) {
+        for(int i=1; i<arr.length; i++){
+            int k = i;
+            for(int j=i-1; j>=0 && less((Comparable<E>) arr[k], arr[j]); j--){
+                exch(arr, k, j);
+                k = j;
             }
         }
-
-    }
-
-
     }
+}
 

module5/src/main/java/com/hithomelabs/princeton1/module5/Selection.java

@@ -1,23 +1,20 @@
 package com.hithomelabs.princeton1.module5;
 
-
+/*
+ * * Selection sort "selects" the smallest element and swaps it with arr[0] of the array
+ * * Then proceeds to do the same swapping arr[i] with arr[i:arr.length-1]
+ */
 public class Selection<E> extends AbstractCustomSorts<E>{
-
-    /*
-    * * Selection sort "selects" the smallest element and swaps it with arr[0] of the array
-    * * Then proceeds to do the same swapping arr[i] with arr[i:arr.length-1]
-    */
-    public void sort(E[] arr){
-        if (arr ==  null) return;
-        Comparable<E>[] arr1 = (Comparable<E>[]) arr;
-        for(int i = 0; i < arr1.length - 1; i++){
+    @Override
+    public void sort(E[] arr) {
+        for (int i = 0; i < arr.length; i++) {
             int minIndex = i;
-            for(int j = i+1; j < arr.length; j ++){
-                if (less((Comparable<E>) arr[j], arr[minIndex])) minIndex = j;
+            for(int j = i+1; j < arr.length; j++){
+                if(less((Comparable<E>) arr[j], arr[minIndex]))
+                    minIndex = j;
             }
             exch(arr, i, minIndex);
         }
     }
-
 }
 

module5/src/main/java/com/hithomelabs/princeton1/module5/Shell.java

@@ -25,32 +25,37 @@ public class Shell<E> extends AbstractCustomSorts<E> {
     @Override
     public void sort(E[] arr) {
         MetaData metaData = new MetaData();
-        int N = arr.length;
+
         int h = 1;
-        // * * Calculates the largest value of h greater than n
-        while (3 * h + 1 < N) {
-            h = 3 * h + 1;
+        while(3*h + 1 < arr.length){
+            h = 3*h + 1;
         }
-        while (h >= 1) {
-            h = hsort(arr, h, metaData);
-            h = h / 3;
+        while(h>=1){
+            hsort(arr, h, metaData);
+            h= h/3;
         }
+//        for(int i=arr.length/10; i>=0; i--){
+//            hsort(arr, 3*i+1, metaData);
+//        }
         System.out.println("Array sorted (shell sort) with " + metaData.compares + " compares and " + metaData.swaps + " swaps");
     }
 
-    private int hsort(E[] arr, int h, MetaData metadata) {
-        int N  = arr.length;
-        for(int i = h; i < N; i++){
-            int j = i;
-            ++metadata.compares;
-            while(j >= h && less((Comparable<E>) arr[j], arr[j-h])){
-                ++metadata.swaps;
-                exch(arr, j, j-h);
-                j = j - h;
-                ++metadata.compares;
+    private void hsort(E[] arr, int h, MetaData metadata) {
+        for(int i=h; i<arr.length; i=i+1){
+            int k = i;
+            for(int j=i-h; j>=0; j=j-h){
+                metadata.compares++;
+                if(less((Comparable<E>) arr[k], arr[j])){
+                    exch(arr, k, j);
+                    k = j;
+                    metadata.swaps++;
+                }
+                else{
+                    break;
+                }
+
             }
         }
-        return h;
     }
     /*
      * Sample implementation of insertion sort as h-sort of h = 1
@@ -59,7 +64,7 @@ public class Shell<E> extends AbstractCustomSorts<E> {
     public void insertionSort(E[] arr){
         MetaData metaData = new MetaData();
         int h = 1;
-        h = hsort(arr, h, metaData);
+        hsort(arr, h, metaData);
         System.out.println("Array sorted (insertion sort) with " + metaData.compares + " compares and " + metaData.swaps + " swaps");
     }
 

module6/src/main/java/com/hithomelabs/princeton1/module6/Merge.java

@@ -5,40 +5,40 @@ import com.hithomelabs.princeton1.module5.AbstractCustomSorts;
 import java.util.Arrays;
 
 public class Merge<E> extends AbstractCustomSorts<E> {
+    private E[] auxArr;
+
     @Override
     public void sort(E[] arr) {
-
-        int N = arr.length;
-        // * * aux is a helper array required for merge
-        E[] aux = Arrays.copyOf(arr, N);
-        mergesort(arr, aux, 0, N-1);
-
+        auxArr = (E[]) new Object[arr.length];
+        merge_sort(arr, 0, arr.length-1);
     }
 
-    private void mergesort(E[] arr, E[] aux, int lo, int hi) {
+    private void merge_sort(E[] arr, int low_index, int high_index){
+        if(high_index - low_index > 0) {
+            int mid_index = low_index + (high_index - low_index)/2;
+            merge_sort(arr, low_index, mid_index);
+            merge_sort(arr, mid_index + 1, high_index);
 
-        if (hi <= lo) return;
-        int mid = lo + (hi - lo)/2;
-        mergesort(arr, aux, lo, mid);
-        mergesort(arr, aux, mid+1, hi);
-        merge(arr, aux, lo, mid, hi);
+            // Copy array
+            for(int i=low_index; i<= high_index; i++)
+                auxArr[i] = arr[i];
 
-    }
-
-    private void merge(E[] arr, E[] aux, int lo, int mid, int hi) {
-
-        // * * creating backup of original array
-        for (int i = lo; i <= hi; i++)
-            aux[i] = arr[i];
-
-        int i = lo;
-        int j = mid+1;
-        for (int k = lo; k <= hi; k++){
-            // * If i has already reached mid, no need to compare we insert at pointer k
-            if(i > mid) arr[k] = aux[j++];
-            else if(j > hi) arr[k] = aux[i++];
-            else if(less((Comparable<E>) aux[i], aux[j])) arr[k] = aux[i++];
-            else arr[k] = aux[j++];
+            // Sort
+            int low_index_ptr = low_index;
+            int mid_index_ptr = low_index + (high_index - low_index)/2;
+            int high_index_ptr = mid_index_ptr + 1;
+            if(!less((Comparable<E>) auxArr[mid_index_ptr], auxArr[high_index_ptr])) {
+                for (int i = low_index; i <= high_index; i++) {
+                    if (low_index_ptr > mid_index_ptr) {
+                        arr[i] = auxArr[high_index_ptr++];
+                    } else if (high_index_ptr > high_index)
+                        arr[i] = auxArr[low_index_ptr++];
+                    else if (less((Comparable<E>) auxArr[low_index_ptr], auxArr[high_index_ptr]))
+                        arr[i] = auxArr[low_index_ptr++];
+                    else
+                        arr[i] = auxArr[high_index_ptr++];
+                }
+            }
         }
     }
 }

module7/src/main/java/com/hithomelabs/princeton1/module7/Quick.java

@@ -6,49 +6,45 @@ import com.hithomelabs.princeton1.module5.AbstractCustomSorts;
 public class Quick<E> extends AbstractCustomSorts<E> {
     @Override
     public void sort(E[] arr) {
-        int N = arr.length;
-        quickSort(arr, 0, N - 1);
+        randomShuffle(arr);
+        partition(arr, 0, arr.length-1);
     }
 
-    public void altSort(E[] arr) {
-        int N = arr.length;
-        altQuickSort(arr, 0, N-1);
+    private void randomShuffle(E[] arr){
+        int array_len = arr.length;
+        for(int i=0; i< array_len; i++){
+            int random_index = (int)(Math.random()*array_len);
+            exch(arr, i, random_index);
+        }
     }
 
-    private void altQuickSort(E[] arr, int lo, int hi) {
-        if (lo >= hi) return;
-        int i = lo + 1;
-        int j = i;
-        while(j <= hi){
-            if(less((Comparable<E>) arr[j], arr[lo])){
-                exch(arr, i, j);
+    private void partition(E[] arr, int low, int high){
+        if(low >= high)
+            return;
+        int mid = sort(arr, low, high);
+        partition(arr, low, mid-1);
+        partition(arr, mid + 1, high);
+    }
+
+    private int sort(E[] arr, int low, int high){
+        int i = low+1;
+        int j = high;
+        while (true){
+            // Find the i index greater than 1st element
+            while (i<=high && !less((Comparable<E>) arr[low], arr[i]))
                 i++;
-            }
-            j++;
+            // Find the j index less than 1st element
+            while (less((Comparable<E>) arr[low], arr[j]) && j > low)
+                j--;
+            // Break if indexes are crossed
+            if(j < i)
+                break;
+            // Swap index values of i & j
+            if(less((Comparable<E>) arr[j], arr[i]))
+                exch(arr, i, j);
         }
-        exch(arr, i-1, lo);
-        altQuickSort(arr, lo, i-2);
-        altQuickSort(arr, i, hi);
-    }
-
-    private void quickSort(E[] arr, int lo, int hi) {
-
-        if (lo >= hi) return;
-        int i = lo;
-        int j = hi+1;
-        while(true){
-            while(less((Comparable<E>) arr[++i], arr[lo])){
-                if(i == hi) break;
-            }
-            while(!less((Comparable<E>) arr[--j], arr[lo])){
-                if (j == lo ) break;
-            }
-            if(j<=i) break;
-            exch(arr, i , j);
-        }
-        exch(arr, j, lo);
-        quickSort(arr, lo, j-1);
-        quickSort(arr, j+1, hi);
-
+        // Swap 1st element to it's correct position
+        exch(arr, low, j);
+        return j;
     }
 }

module7/src/test/java/com/hithomelabs/princeton1/module7/QuickTest.java

@@ -33,6 +33,8 @@ class QuickTest {
         Assertions.assertArrayEquals(sorted, arr);
     }
 
+    // * * Optional test for alternate sort implmentation
+    /*
     @Test
     @DisplayName("testing Quick sort default implementation")
     public void testAltSort(){
@@ -45,6 +47,8 @@ class QuickTest {
         Apple[] sorted =  apples.toArray(new Apple[apples.size()]);
         Assertions.assertArrayEquals(sorted, arr);
     }
+    */
+
 
 
     @AfterEach