Input : arr[] = {7, 3, 2, 4, 9, 12, 56} 
        m = 3
Output: Minimum Difference is 2
We have seven packets of chocolates and
we need to pick three packets for 3 students
If we pick 2, 3 and 4, we get the minimum
difference between maximum and minimum packet
sizes.

Input : arr[] = {3, 4, 1, 9, 56, 7, 9, 12} 
        m = 5
Output: Minimum Difference is 6
The set goes like 3,4,7,9,9 and the output 
is 9-3 = 6

Input : arr[] = {12, 4, 7, 9, 2, 23, 25, 41,
                 30, 40, 28, 42, 30, 44, 48, 
                 43, 50} 
        m = 7
Output:  Minimum Difference is 10
We need to pick 7 packets. We pick 40, 41,
42, 44, 48, 43 and 50 to minimize difference
between maximum and minimum.