Update prime_game.md

Author: sreelakshmig009

Techgig Code Gladiators 2021/open round/prime_game.md

@@ -12,5 +12,70 @@ Rax will randomly provide you a range [ L , R ] (both inclusive) and you have to
   <li>There is only one distinct prime number in the given range. The maximum difference in this case would be 0.</li>
   <li>There are no prime numbers in the given range. The output for this case would be -1.</li>
 </ol>
+
+To win the game, the participant should answer the prime difference correctly for the given range.
+
+#### Example:
+
+##### Range: [ 1, 10 ]:
+
+The maximum difference between the prime numbers in the given range is 5.
+Difference = 7 - 2 = 5
+
+##### Range: [ 5, 5 ]:
+
+There is only one distinct prime number so the maximum difference would be 0.
+
+##### Range: [ 8 , 10 ]:
+
+There is no prime number in the given range so the output for the given range would be -1.
+
+Can you win the game?
+
+<b>Input Format:</b>
+
+The first line of input consists of the number of test cases, T
+Next T lines each consists of two space-separated integers, L and R
+
+<b>Constraints:</b>
+
+1<= T <=10
+2<= L<= R<=10^6
+
+<b>Output Format</b>
+
+For each test case, print the maximum difference in the given range in a separate line. 
+
+##### Sample Test Case:
+
+Input:
+```
+5
+5 5
+2 7
+8 10
+10 20
+4 5
+```
+Output:
+```
+0
+5
+-1
+8
+0
+```
+Explanation:
+```
+Test Case 1: [ 5 - 2 ] = 3
+
+Test Case 2: [ 7 - 2 ] = 5
+
+Test Case 3: No prime number in the given range. Output = -1
+
+Test Case 4: [ 19 - 11 ] = 8
+
+Test Case 5: The difference would be 0 since there is only one prime number in the given range.
+```