feat(linked-list): Implement LinkedLists and Recursive LinkedLists

java/src/data_structures/linear/linked_list/CircularDoubleLinkedList.java

@@ -0,0 +1,255 @@
+package data_structures.linear.linked_list;
+
+/**
+ * A class that implements a list of objects using a Circular Double Linked List
+ * 
+ * @author bjornmelin
+ * @param <T> Type of Object to Store in List
+ */
+public class CircularDoubleLinkedList<T> implements ListInterface<T> {
+
+ private Node firstNode;
+ private int numberOfEntries;
+
+ /**
+ * Default constructor for Circular Double Linked List
+ */
+ public CircularDoubleLinkedList() {
+ initializeDataFields();
+ }
+
+ // Initializes the class's data fields to indicate an empty list.
+ private void initializeDataFields() {
+ firstNode = null;
+ numberOfEntries = 0;
+ }
+
+ /**
+ * toString method for Circular Double Linked List
+ * 
+ * @return String denoting all values in the list
+ */
+ public String toString() {
+ String output = "Data in the list(" + getLength() + "):\n";
+ Node curr = firstNode;
+ for (int i = 1; i <= numberOfEntries; i++) {
+ output += "\t" + (i) + ":\t" + curr.data + "\n";
+ curr = curr.next;
+ }
+ return output;
+ }
+
+ @Override
+ public void add(T newEntry) {
+ Node newNode = new Node();
+ newNode.data = newEntry;
+ Node curr = firstNode;
+ newNode.next = null;
+ if (firstNode == null) {
+ newNode.previous = newNode;
+ firstNode = newNode;
+ numberOfEntries++;
+ return;
+ }
+ for (int i = 1; i < numberOfEntries; i++) {
+ curr = curr.next;
+ }
+ if (numberOfEntries == 1) {
+ newNode.previous = firstNode;
+ } else {
+ newNode.previous = curr;
+ }
+ curr.next = newNode;
+ firstNode.previous = newNode;
+ numberOfEntries++;
+ }
+
+ @Override
+ public void add(int newPosition, T newEntry) {
+ if (newPosition >= numberOfEntries) {
+ add(newEntry);
+ } else if (newPosition <= 1) {
+ Node newNode = new Node();
+ newNode.data = newEntry;
+ newNode.next = firstNode;
+ firstNode.previous = newNode;
+ firstNode = newNode;
+ numberOfEntries++;
+ Node curr = firstNode;
+ for (int i = 1; i < numberOfEntries; i++) {
+ curr = curr.next;
+ }
+ newNode.previous = curr;
+ } else {
+ Node curr = firstNode;
+ for (int i = 1; i < newPosition - 1; i++) {
+ curr = curr.next;
+ }
+ Node newNode = new Node();
+ newNode.data = newEntry;
+ newNode.next = curr.next;
+ curr.next = newNode;
+ newNode.previous = curr;
+ if (curr.next.next != firstNode) {
+ curr.next.next.previous = newNode;
+ } else if (curr.next.next == firstNode) {
+ curr.next.next = firstNode;
+ }
+ numberOfEntries++;
+ }
+ }
+
+ @Override
+ public T remove(int givenPosition) {
+ if (numberOfEntries == 0) {
+ return null;
+ }
+ if (givenPosition >= numberOfEntries) {
+ givenPosition = numberOfEntries;
+ } else if (givenPosition <= 1) {
+ givenPosition = 1;
+ }
+ if (givenPosition == 1) {
+ Object temp = firstNode.data;
+ firstNode = firstNode.next;
+ firstNode.previous = null;
+ numberOfEntries--;
+ return (T) temp;
+ }
+ Node curr = firstNode;
+ for (int i = 1; i < givenPosition - 1; i++) {
+ curr = curr.next;
+ }
+ Object temp = curr.next.data;
+ curr.next.next.previous = curr;
+ curr.next = curr.next.next;
+ numberOfEntries--;
+ return (T) temp;
+ }
+
+ @Override
+ public void clear() {
+ initializeDataFields();
+ }
+
+ @Override
+ public T replace(int givenPosition, T newEntry) {
+ if (givenPosition <= 1) {
+ Object temp = firstNode.data;
+ firstNode.data = newEntry;
+ return (T) temp;
+ }
+ if (givenPosition > numberOfEntries) {
+ givenPosition = numberOfEntries;
+ }
+ Node curr = firstNode;
+ for (int i = 1; i < givenPosition; i++) {
+ curr = curr.next;
+ }
+ Object temp = curr.data;
+ curr.data = newEntry;
+ return (T) temp;
+ }
+
+ @Override
+ public T getEntry(int givenPosition) {
+ if (numberOfEntries <= 0) {
+ return null;
+ } else if (givenPosition >= numberOfEntries) {
+ givenPosition = numberOfEntries;
+ } else if (givenPosition <= 1) {
+ givenPosition = 1;
+ }
+ Node curr = firstNode;
+ for (int i = 1; i < givenPosition; i++) {
+ curr = curr.next;
+ }
+ return (T) curr.data;
+ }
+
+ @Override
+ public T[] toArray() {
+ @SuppressWarnings("unchecked")
+ T[] output = (T[]) new Object[numberOfEntries];
+ Node curr = firstNode;
+ for (int i = 1; i < numberOfEntries; i++) {
+ output[i] = (T) curr.data;
+ curr = curr.next;
+ }
+ return output;
+ }
+
+ @Override
+ public boolean contains(T anEntry) {
+ Node curr = firstNode;
+ while (curr != null) {
+ for (int i = 1; i < numberOfEntries; i++) {
+ if (curr.data == anEntry) {
+ return true;
+ }
+ curr = curr.next;
+ }
+ }
+ return false;
+ }
+
+ @Override
+ public int getLength() {
+ return numberOfEntries;
+ }
+
+ @Override
+ public boolean isEmpty() {
+ return numberOfEntries <= 0;
+ }
+
+ @Override
+ public void reverseData() {
+ Node curr = firstNode;
+ for (int i = 1; i < numberOfEntries; i++) {
+ curr = curr.next;
+ }
+ System.out.println("The last item on the list is " + curr.data);
+ System.out.println("Moving down the nodes in the list in reverse order: ");
+ for (int i = 0; i < numberOfEntries; i++) {
+ System.out.println("Present Node Data: " + curr.data);
+ curr = curr.previous;
+ }
+ }
+
+ @Override
+ public void circleTest() {
+ System.out.println("We are testing the values to see if it is a circular loop.");
+ System.out.println("Starting at the first node, we will loop backwards 2 times.");
+ Node curr = firstNode;
+ for (int i = 0; i < numberOfEntries * 2; i++) {
+ System.out.println("Present Node Data: " + curr.data);
+ curr = curr.previous;
+ }
+ }
+
+ private class Node {
+ T data;
+ Node next;
+ Node previous;
+ }
+
+ private Node getNodeAt(int givenPosition) {
+ assert !isEmpty() && (1 <= givenPosition) && (givenPosition <= numberOfEntries);
+ Node currentNode = firstNode;
+ currentNode = find(0, givenPosition, currentNode);
+ assert currentNode != null;
+ return currentNode;
+ }
+
+ private Node find(int count, int index, Node curr) {
+ if (curr == null) {
+ return null;
+ }
+ count++;
+ if (count == index) {
+ return curr;
+ }
+ return find(count, index, curr.next);
+ }
+}