add quicksort under divide and conquer

[OmMahajan29]

Feature description

would like to add quicksort algo under divide and conquer

[tianyizheng02]

We already have multiple implementations of quick sort in this repo. We do not want duplicate implementations of existing algorithms. Furthermore, please read our contributing guidelines. We do not assign issues in this repo, and contributors should not create issues to suggest new algorithms.

If you are interested in resolving an open issue, simply make a pull request with your proposed fix. We do not assign issues in this repo so please do not ask for permission to work on an issue.

Do not create an issue to contribute an algorithm. Please submit a pull request instead.