Unique value in an array?

So, someone recently told me about an interview question they heard about for some job at Amazon. I thought the question and answer were neat, so I figured I'd share it.

The question goes: "If you were given an array filled with a bunch of numbers, where every number was duplicated exactly one time except for one number, which is only in the array once, what is the most efficient way to find the unique value?"

The answer is to iterate through the array one time, performing XOR on each of the numbers. At the end, the value you have will be the unique value.

Want to see it for yourself?

Here's a JavaScript snippet I wrote to prove it on a smaller scale. This will work on arrays of any size, however.



Speaking of XOR and interview questions, I was a part of creating the team test we give people who want to join our team, and one of the questions was to have the person write a piece of code that would swap variable values without using a 3rd variable as a "value bucket". I decided to try to do this in one line using XOR, and I pulled it off.

The JS for it is:

It's been a while!

It truly has been a while since I have posted anything here. To be quite honest, I have immersed myself in so much JavaScript best practices, new patterns, performance optimization, etc, that I have highly neglected this blog!

Since my last few posts, I have increased in my JS knowledge IMMENSELY, and that is no joke. I am w3schools certified (link to cert) *with excellence*. I got 69 of the 70 questions right! Woo hoo!

I have studied very carefully presentations, books, papers, etc from various JS gurus, Nicholas Zakas, Douglas Crockford, John Resig, etc. I actually printed out the current ECMAScript specification and read it on a flight to Las Vegas for a team meeting.

I am not joking when I say this, JavaScript is one of my biggest passions. If I could do nothing but analyze problems and engineer solutions in JavaScript all day long, I would do it!

Unfortunately, there isn't really that great of a job market that I can find. I don't have any degrees as of yet, and the area I live in really kind of prevents me from finding any solid JS jobs, and it'd be REALLY hard for me to relocate.

Members on my team at work think I'm really good at JS, and I think I'm pretty good, too. I'd like to be able to focus solely on that, as it is easily my biggest strength, but it's really hard to do that right now.

I'll keep it as a hobby, and maybe one day, I'll find a JS engineering job to call my home.

In other news, I am going to check out Dojo. I've been using jQuery for a very long time now, and I'm interested to dive into another JS library. I like what Dojo brings to the table. I haven't had a chance to dive into the source just yet, but at face value, it promises to offer some really neat functionality.

I am in the process of checking out the repository for the source now (it's huge). I like to dive into source code when I'm picking something new up.

I also purchased a book called Mastering Dojo: JavaScript and Ajax Tools for Great Web Experiences to read over the next few days.

I'm excited to really dig in and learn some new stuff!