Update README.md

Author: Developer-Rakeen

README.md

@@ -12,3 +12,7 @@ I hope you all would be very benefitted by going through this repository.
 
 #### *Data Structures* 👇
 1. [Arrays - DS](https://www.hackerrank.com/challenges/arrays-ds/problem/)
+2. [2D Array - DS](https://www.hackerrank.com/challenges/2d-array/problem?isFullScreen=true)
+3. [Left Rotation](https://www.hackerrank.com/challenges/array-left-rotation/problem?isFullScreen=true)
+4. [Sparse Arrays](https://www.hackerrank.com/challenges/sparse-arrays/problem?isFullScreen=true)
+5. [Print the Elements of a Linked List](https://www.hackerrank.com/challenges/print-the-elements-of-a-linked-list/problem?isFullScreen=true)