Finally Divide and Conquer section is finished. A lot of work but so
much fun!

A few take aways:
1. Be careful when copying code over from Java to C++. Java does
parameter passing through reference as default, but I forgot to add "&"
in C++ code, which caused my code not passing earlier;
2. Avoid unnecessary calculation. For example, the sqrt calculation is
not necessary, until the last step. Avoiding that in my Python code
saved a lot of time.
3. It seems that preallocate vector size, if you know beforehand, is a
good idea.

Woohoo, onto the next section!

Really fun to implement it in C++. Learned std::sort, std::unique, ==
overloading for struct for std::unique to work. Good stuff!

Good exercise. Learned C++ vector usage, and the ASSERT_NEAR macro for
testing floats/doubles. Lots of fun.