Add solution for 3rd LeetCode Practice Problem - Longest Substring Without Repeating Characters

[Git-Harshit]

Pull Request Template

Description

This commit adds a well-commented and human-readable Python 3 program to solve the third LeetCode Practice Problem viz., "Longest Substring Without Repeating Characters". The code is judged as Accepted on LeetCode, on 1st August 2021 (the same day this PR is initiated). Have a look, and feel free to suggest any changes or directly improvise the solution.

Put check marks:

Have you made changes in README file ?

• Added problem & solution under correct topic.
• Specified Space & Time complexity.
• Specified difficulty level, tag & Note(if any).

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Please also note any relevant details for your test configuration.

• Test A
• Test B
• Directly submitted the solution to LeetCode Judge (Result: Accepted)

Make sure all below guidelines are followed else PR will get Reject:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code so that it is easy to understand
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules

[welcome]

I can tell this is your first pull request! Thank you I'm so honored. 🎉🎉🎉 I'll take a look at it ASAP!

[GouravRusiya30]

Thanks @Git-Harshit
Changes looks fine but can you change the file name of newly added python code to adhere to the naming conventions ?

[Git-Harshit]

Sure @GouravRusiya30, I will update the file name as per your naming convention.
I have looked into your README and CONTRIBUTING files before, but didn't get any code naming convention.

Update: Renamed the file as per naming convention <PROBLEM_NAME>.<FILE_FORMAT> as per the naming guideline mentioned in PULL_REQUEST_PROCESS file. I hope it's adhering to the naming conventions now. Please let me know if anything else can be improvised.

[GouravRusiya30]

Thanks for updating the file name but you haven't updated the README with correct path of file.

[Git-Harshit]

Oops, My bad! I did forget about it. Thanks for pinging me on it. I have updated it on the README file too, please have a look again, it should be fine now. 🙂

[welcome]

Your code looks great! Congrats, I've gone ahead and merged your first pull request! Keep it up!