add graph algorithms

[rohanprasadofficial]

[Shadman-Ahmed-Chowdhury]

I would like to be assigned.

[adarsh1mehra]

hi, owner ! i wanna work this on project, kindly assign me this !

[samkit96]

Hi, Can I work on Floyd Warshall Algorithm?

[rohanprasadofficial]

Hey Everyone, you all write clean code and do a PR I will review them once tonight and approve them if its a good once?

Make sure that you don't add duplicate requests.

Remember to add code in C++ as it is a C++ codebase.

[shivam2001pandey]

@rohanprasadofficial I have added Graph algorithm .Kindly have a look into it. Please Merge it.
Thank you.