addAt(index, data) function added

This function is intended to add a node of a specified data element to a particular index in the linked list.

Author: Prashansa-K

com/williamfiset/algorithms/datastructures/linkedlist/DoublyLinkedList.java

@@ -77,6 +77,38 @@ public void addFirst(T elem) {
     size++;
   }
 
+  // Add an element at a specified index
+  public void addAt(int index, T data) throws Exception
+	{
+		if(index<0)
+		{
+			throw new Exception("Illegal Index");
+		}
+		if(index==0)
+		{
+			addFirst(data);
+			return;
+		}
+		
+		if(index==size)
+		{
+			addLast(data);
+			return;
+		}
+		
+		Node<T> temp=head;
+		for(int i=0;i<index-1;i++)
+		{
+			head=head.next;
+		}
+		Node<T> newNode = new Node(data,null,null);
+		newNode.next=head.next;
+		newNode.prev=head.prev;
+		head.next=newNode;
+		head=temp;
+		
+		size++;
+	}
   // Check the value of the first node if it exists, O(1)
   public T peekFirst() {
     if (isEmpty()) throw new RuntimeException("Empty list");