Add C++ solutions for the entire NeetCode 150 list

[paolo-torres]

Hey NeetCode :)

Just finished up going through the NeetCode 150 list so I thought I might as well contribute my C++ code here. All solutions have the following format:

Short description of the problem.
Examples of input and expected output.

Short description of the intuition behind how to solve the problem.

Time Complexity
Space Complexity

{CODE}

All solutions pass on LeetCode, are optimal or near optimal in time and space, and are clean/readable/have comments/all that jazz. Some also have multiple approaches commented out for some alternate solutions. The folders are also numbered such that they line up with the list on the website.

Keep up the great content!

[neetcode-gh]

Hey, thank you so much this is great!!!