Install VirtualBox on Fedora

To solve DKMS failure:

yum install gcc kernel-devel kernel-headers
 
## PAE kernel users install ##
yum install gcc kernel-PAE-devel kernel-headers

Add VirtualBox User to vboxusers Group

usermod -a -G vboxusers user_name

Quicksort

"The quicksort algorithm has a worst-case running time of  Θ(n^2 ) on an input array of n numbers. Despite this slow worst-case running time, quicksort is often the best practical choice for sorting because it is remarkably efficient on the average: its expected running time is Θ(nlgn), and the constant factors hidden in the Θ(nlgn) notation are quite small. It also has the advantage of sorting in place, and it works well even in virtual-memory environments."  [Introduction to algorithms]