thmain

public class GoldbachConjecture {

	public static void Goldbach(int x) {
		if (x % 2 != 0) {
			System.out.println("Not Even");
			return;
		}
		if (x <= 2) {
			System.out.println("Less than 2");
			return;

thmain

public class isBST {
	public static Node prevNode = null;

	// method 1: do inOrder and check if it is in ascending order
	// doesnt work in case of duplicates
	public boolean isBST1(Node root) {
		if (root != null) {
			if (!isBST1(root.left))
				return false;
			if (prevNode != null && prevNode.data >= root.data) {

thmain

public class CircularLinkedList {

    public int size =0;
    public Node head=null;
    public Node tail=null;

    //add a new node at the start of the linked list
    public void addNodeAtStart(int data){
        System.out.println("Adding node " + data + " at start");

thmain

public class DoublyLinkedList {

    int size =0;
    Node head = null;
    Node tail = null;

    public Node addAtStart(int data){
        System.out.println("Adding Node " + data + " at the start");
        Node n = new Node(data);
        if(size==0){

thmain

public class NthNodeFromEnd {
    //Method 1
    //Get the length of the Linked list, say it x
    //nth node from the end will be x-n+1 from the start of the linked list
    public static int getNodeUsingLength(Node head, int n){
        int x =0;
        Node curr = head;
        while(curr!=null){
            x++;

thmain

public class DiameterOfTree {

	public int getHeight(Node root) {
		if (root != null) {
			return 1 + Math.max(getHeight(root.left), getHeight(root.right));
		}
		return 0;
	}

	public int Diameter(Node root) {

thmain

public class DiameterOfTree {
	int diameter = 0;

	// here in improved solution, we calculate the height and diameter for every
	// node in same iteration
	// every Node will return 2 values, diameter and height wrt to the
	// particular node
	public int[] Diameter(Node root) {
		int DandH[] = { 0, 0 }; // initialize the height (DandH[0]) and diameter
								// as 0 (DandH[1])

thmain

public class StackUsingLinkedList {
    Node head= null;
    int size =0;

    public void push(int data){
        Node x = new Node(data);
        if(getSize()==0){
            head = x;
        }else{
            //add the Node at the start of a Linked List

thmain

import java.util.Hashtable;

public class SimpleHashTable {

	int [] a = new int[5];

	String [] arrNames = new String[]{"Sumit","Jain","Raghav","Garg","Gaurav","Rishi"};

	Hashtable<Integer, String> ht = new Hashtable<Integer, String>();

thmain

public class RearrageArrayPositiveNegative {
	int[] arrA;

	public RearrageArrayPositiveNegative(int[] arrA) {
		this.arrA = arrA;
	}

	public void divideGroups(int low, int high) {
		if (low >= high)
			return;