Implement "Linear Median Finding"

[tigercosmos]

I am going to implement this one.
Which category do you want it to belong with?

Reference:
https://rcoh.me/posts/linear-time-median-finding/
https://en.wikipedia.org/wiki/Median_of_medians

[weihanglo]

Wow. It's a good question. Selection algorithms use a mix of searching and sorting (and many others). Seems that it cannot fit any of current categories. Maybe we can add a new category named "selection" and add more algorithms into.