added approach 3 of 6 in java

Java/Data-Structures/LISTS/MISC/Nth-node-from-end/Approach3.java

@@ -0,0 +1,150 @@
+import java.util.*;
+abstract class Approach3
+{
+    /**
+     * LINKED LIST CLASS
+     **/
+    private static class LinkedList
+    {
+        /**
+         * NODE CLASS
+         * for linked list node
+         **/
+        private class Node
+        {
+            private int data;
+            private Node next;
+
+            //constructor
+            public Node(int data)
+            {
+                this.data=data;
+                next=null;
+            }
+
+            /**
+             * getData()
+             * @return data in the node
+             **/
+            public int getData()
+            {
+                return data;
+            }
+
+            /**
+             * getNext()
+             * @return the next node 
+             **/
+            public Node getNext()
+            {
+                return next;
+            }
+
+            /**
+             * setNext()
+             * @param next
+             **/
+            public void setNext(Node next)
+            {
+                this.next=next;
+            }
+        }
+
+        private Node head;  //head of the linked list
+
+        //constructor for linked list
+        public LinkedList()
+        {
+            head=null;
+        }
+
+        /**
+         * insert_at_head()
+         * it will insert node at the head of the linked list
+         * @param data
+         **/
+        public void insert_at_head(int data)
+        {
+            Node newNode = new Node(data);
+            if(head==null)
+            {
+                head=newNode;
+            }
+            else
+            {
+                newNode.setNext(head);
+                head=newNode;
+            }
+        }
+
+        /**
+         * print_list()
+         * it will print the linked list
+         **/
+        public void printList()
+        {
+            if(head==null)
+            {
+                System.out.println("NULL");
+            }
+            else
+            {
+                Node current=head;
+                while(current!=null)
+                {
+                    System.out.print(current.getData() +" -> ");
+                    current=current.getNext();
+                }
+                System.out.println("NULL");
+            }
+        }
+
+        /*====================================================================*/
+        /**
+         * APPROACH 3
+         * Using hashtable
+         * traverse the list and make hashtable
+         * we will get the size of the list
+         * we will calculate nth node from hashtable by substracting the nthnode from size
+         **/
+        public void printNthNodeFromLast(int num)
+        {
+            int[] hash = new int[10];   //hashtable
+            int size=0;
+            Node current=head;
+
+            while(current!=null)    //traversing and making hashtable
+            {
+                hash[size]=current.getData();
+                current=current.getNext();
+                size++;
+            }
+            if(num>size)
+            {
+                System.out.println("INDEX OUT OF BOUNDS");
+                return;
+            }
+            System.out.println(hash[size-num]);
+        }
+        /*====================================================================*/
+    }
+
+    public static void main(String[] args)
+    {
+        LinkedList ll = new LinkedList();
+        ll.insert_at_head(3);
+        ll.insert_at_head(1);
+        ll.insert_at_head(4);
+        ll.insert_at_head(2);
+        ll.insert_at_head(5);
+
+        ll.printList();
+
+        Scanner in = new Scanner(System.in);
+        System.out.println("Enter the nth node from last");
+        int n = in.nextInt();
+
+        ll.printNthNodeFromLast(n);
+        in.close();
+    }
+}

Java/README.md

@@ -42,7 +42,7 @@
   * Find the nth node from end in single linked list
     * APPROACH 1: [Compute the size while adding](Data-Structures/LISTS/MISC/Nth-node-from-end/Approach1.java)
     * APPROACH 2: [Using two current pointers](Data-Structures/LISTS/MISC/Nth-node-from-end/Approach2.java)
-    * APPROACH 3: Using hashtable
+    * APPROACH 3: [Using hashtable](Data-Structures/LISTS/MISC/Nth-node-from-end/Approach3.java)
     * APPROACH 4: Using Hashtable while adding
     * APPROACH 5: Finding node in one scan
     * APPROACH 6: Using recursion