Added links to all the questions for reference

Author: myang310

CrackingtheCodeInterview/QueueAsTwoStacks.java

@@ -10,6 +10,8 @@
 1 x: Enqueue element  into the end of the queue.
 2: Dequeue the element at the front of the queue.
 3: Print the element at the front of the queue.
+
+Link: https://www.hackerrank.com/challenges/ctci-queue-using-two-stacks
 */
 
 import java.io.*;

DynamicProgramming/CoinChange.java

@@ -28,6 +28,8 @@
 If you can think of a way to store the checked solutions, then
 this store can be used to avoid checking the same solution again
 and again.
+
+Link: https://www.hackerrank.com/challenges/coin-change
 */
 
 import java.io.*;

DynamicProgramming/FibonacciModified.java

@@ -11,6 +11,8 @@
 but, for those that don't (e.g., C++), you will need to be more creative
 in your solution to compensate for the limitations of your chosen
 submission language.
+
+Link: https://www.hackerrank.com/challenges/fibonacci-modified
 */
 
 import java.io.*;

DynamicProgramming/TheMaximumSubarray.java

@@ -5,6 +5,8 @@
 2. Non-contiguous (not necessarily contiguous) subarray.
 
 Empty subarrays/subsequences should not be considered.
+
+Link: https://www.hackerrank.com/challenges/maxsubarray
 */
 
 import java.io.*;