Add "nice to knows" for LCS and quickselect

[jfceja]

It's nice to know that the LCS problem can be solved in O(n) space using the algorithm made by Hirschberg.

It's nice to know that quick-select can be done in O(n) worst-case (deterministic).

These "more efficient" implementations likely aren't as easy to understand/modify so I get that someone may intentionally choose the ones that you have here

[leetcoder123]

My team just had to swap out the normal quick-select algorithm with the deterministic variant, so I will have to disagree with the general/unqualified claim "is actually not used in practice".