Greg gremz

Conventions

A = [xA, yA] is a point on the 2D plane. Same for B, C, ...
lengths are in any unit (ex: pixels)
code snippets are in JavaScript

Degrees to radians

angleRad = angleDeg * Math.PI / 180;

ANNOUNCEMENT

I have moved this over to the Tech Interview Cheat Sheet Repo and has been expanded and even has code challenges you can run and practice against!

\

Whether you're trying to give back to the open source community or collaborating on your own projects, knowing how to properly fork and generate pull requests is essential. Unfortunately, it's quite easy to make mistakes or not know what you should do when you're initially learning the process. I know that I certainly had considerable initial trouble with it, and I found a lot of the information on GitHub and around the internet to be rather piecemeal and incomplete - part of the process described here, another there, common hangups in a different place, and so on.

In an attempt to coallate this information for myself and others, this short tutorial is what I've found to be fairly standard procedure for creating a fork, doing your work, issuing a pull request, and merging that pull request back into the original project.

Creating a Fork

Just head over to the GitHub page and click the "Fork" button. It's just that simple. Once you've done that, you can use your favorite git client to clone your repo or j

Originally published in June 2008

When hiring Ruby on Rails programmers, knowing the right questions to ask during an interview was a real challenge for me at first. In 30 minutes or less, it's difficult to get a solid read on a candidate's skill set without looking at code they've previously written. And in the corporate/enterprise world, I often don't have access to their previous work.

To ensure we hired competent ruby developers at my last job, I created a list of 15 ruby questions -- a ruby measuring stick if you will -- to select the cream of the crop that walked through our doors.

What to expect

Candidates will typically give you a range of responses based on their experience and personality. So it's up to you to decide the correctness of their answer.

In August 2007 a hacker found a way to expose the PHP source code on facebook.com. He retrieved two files and then emailed them to me, and I wrote about the issue:

http://techcrunch.com/2007/08/11/facebook-source-code-leaked/

It became a big deal:

http://www.techmeme.com/070812/p1#a070812p1

The two files are index.php (the homepage) and search.php (the search page)

Latency numbers every programmer should know

L1 cache reference ......................... 0.5 ns
Branch mispredict ............................ 5 ns
L2 cache reference ........................... 7 ns
Mutex lock/unlock ........................... 25 ns
Main memory reference ...................... 100 ns             
Compress 1K bytes with Zippy ............. 3,000 ns  =   3 µs
Send 2K bytes over 1 Gbps network ....... 20,000 ns  =  20 µs
SSD random read ........................ 150,000 ns  = 150 µs

Read 1 MB sequentially from memory ..... 250,000 ns = 250 µs

	#XLarge DBInstanceClassMemory = 15892177440 = 14.8GB
	#/32 = 496630545 = 473MB
	#/64 = 248315272 = 236MB
	#/128 = 124157636 = 118MB
	#/256 = 62078818 = 59MB
	#/512 = 31039409 = 29MB
	#/12582880 = 1263 #default same divisor as max_connections = 4041.6MB = 4237924762
	#/25165760 = 623 # half of max_connections = 1993.6MB
	#/50331520 = 315 # quarter of max_connections = 1008MB = 1056964608
	#*(3/4) #default innodb pool size = 11922309120

	if "[email protected]" =~ /@(.*)/
	$1
	else
	raise "bad email"
	end
	# => "example.com"

	# Video: http://rubyhoedown2008.confreaks.com/08-chris-wanstrath-keynote.html

	Hi everyone, I'm Chris Wanstrath.

	When Jeremy asked me to come talk, I said yes. Hell yes. Immediately. But
	then I took a few moments and thought, Wait, why? Why me? What am I supposed
	to say that's interesting? Something about Ruby, perhaps. Maybe the
	future of it. The future of something, at least. That sounds
	keynote-y.