pgf VS pgfplots

The pgf/TikZ manual

In the past I have used TikZ & PGF. You can make just about any diagram with this tool. I don't know of a package that will do what you want, but you can search CTAN. The latest manual is here: https://github.com/pgf-tikz/pgf/releases

My guess would be TikZ.

LaTeX can also let you create flow charts and all other sorts of diagrams through the TikZ package.

PGF/TikZ comes to mind.

But, if you really hate yourself and the self-flagellation doesn’t suit your fancy, you can find a primer on the basics of programming in LaTeX here: https://pgfplots.sourceforge.net/ (look for the technical papers) I did the solving part the most basic, brute force way possible—it was already obnoxious enough. Modern computers are fast enough for even the LaTeX to come up with a solution in a reasonable time frame (still, think minutes, not seconds). I’m sure somebody who actually cares about such things will be able to point you towards something much more sane, but that unfortunately won’t be me.

But if you're looking for a comprehensive list of the out-of-box keys, you might try looking through the pgfplots repo.

The TikZ library colorbrewer doesn't define a color Dark2-3-2 but it does have Dark2-A through Dark2-H, and the PGF library colorbrewer organizes those into colormaps, so you can lookup the color map and use the desired colors:

You’ve clearly either not read the source code for any complex LaTeX package or haven’t understood it. Your criterion is ‘data structures and algorithms’? Well, here’s a data structure, and I’m sure if I dig around for a couple of minutes I can find an algorithm. The PGFPlots maintainer has the package on his resumé, and he has a job. Even if he didn’t, that’s clearly an unnecessary criterion. You’re unlikely to be hired on the basis of your MACRO-11 knowledge. That doesn’t stop it being programming.