Add C++ Solutions

[Anshul1507]

• Longest Substring without repeating characters
• Reverse Integer

[fishercoder1534]

LGTM, but please:

1. number each solution, e.g. solution1, solution2, etc. for the same problem;
2. separate commits into their individual PRs, it's preferred one PR for one problem/solution to minimize code changes so that easier to track;

Thanks!

[Anshul1507]

@fishercoder1534 Done with the first change and will create separate PRs for each solution from next time. 👍