How to find Nth node from the end of a Singly Linked List in Java?

In This Post, We will learn How to find Nth node from the end of a Singly Linked List in Java?

Complete Source code :

Program Logic is Very Simple:

We defined two Node references/Pointers(mainPointer & refPointer) and both will be initialized to the head node.
First iterate refPointer to N nodes.
Then iterate both node pointers (mainPointer & refPointer) one step at a time, till refPointer node is null.
Once Setp-3 is completed, the mainPointer represents the Nth node from the end node

package com.kkjavatutorials.util;

/**
 * How to find Nth node from the end of a Singly Linked List in Java ?
 * @author KK JavaTutorials
 */
public class LinkedList<T> {
	
	private Node<T> head;
	
	//This internal class represents Node in Linked List
	private static class Node<T>{
		
		private T data;
		private Node<T> next;
		public Node(T data) {
			super();
			this.data = data;
			this.next = null;
		}
	}
	
	/**
	 * This method insert a Node in Linked List
	 * @param data has to insert in the List
	 */
	public void insert(T data) {
		Node<T> newNode = new Node<T>(data);
		if(head == null) {
			head = newNode;
		}else {
			Node<T> currentNode = head;
			while (currentNode.next != null) {
				currentNode = currentNode.next;
			}
			 currentNode.next = newNode;
		}
	}
	
	/**
	 * Method which traverse Linked List and display all data.
	 */
	public void displayLinkedList() {
		Node<T> currentNode = head;
		while(currentNode!= null) {
			System.out.print(currentNode.data+" ");
			currentNode = currentNode.next;
		}
	}
	
	/**
	 * This Method returns Nth node from the end of a Singly Linked List in Java
	 * @param n node number from end of a List
	 * @return Nth Node from the end of a List
	 */
	public T findNthNodeFromEnd(int n) {
		if(head == null) {
			return null;
		}
		if(n<=0) {
			throw new IllegalArgumentException("Invalid Value of n ="+n);
		}
		Node<T> mainPointer = head;
		Node<T> refPointer = head;
		int count = 0;
		
		while(count < n) {
			if(refPointer == null) {
				throw new IllegalArgumentException("Valus of n ="+n+" is greater than number of nodes in the list!!");
			}
			refPointer = refPointer.next;
			count++;
		}
		
		while(refPointer !=null) {
			refPointer = refPointer.next;
			mainPointer = mainPointer.next;
		}
		T result = mainPointer.data;
		return result;
		
	}
	
	public static void main(String[] args) {
		
		LinkedList<Integer> linkedList = new LinkedList<>();
		linkedList.insert(10);
		linkedList.insert(20);
		linkedList.insert(30);
		linkedList.insert(40);
		linkedList.insert(50);
		linkedList.insert(60);
		
		System.out.println("Linked List is:");
		linkedList.displayLinkedList();
		
		System.out.println();
		int NthNodeFromEnd = 3;
		
		System.out.println("3rd Node from end of the List is :"+linkedList.findNthNodeFromEnd(NthNodeFromEnd));
		
	}
}

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