How to build Algorithm confidence and where to practice? [closed]

Practice TDD

One of the principles of TDD is that it forces you to think about the structure of your code in ways that makes it testable. Unit testing is all about that: units of code that are individually testable.

Once you get into the mindset of thinking this way, you begin sectioning off your code into little units of functionality. Once each unit is done, you don't have to think about it anymore; you've now got this new little piece of functionality that you can combine with other little pieces of functionality into a larger program.

In addition, because you're required to write the tests first, you are forced to think about your requirements... what is this code supposed to do, and how can I organize these bits of code in a way that will help me achieve my objective?

Study other people's code

One of the best ways to learn about code structure is to study frameworks. Frameworks are all about taking a specific problem, and generalizing it into a library so that it can be applied to a wider range of problems. You can learn a ton about design by examining those frameworks.

In addition, many common problems have been formalized into software design patterns. Study those. I'm not just talking about the GOF patterns; I'm also talking about things like Object-Oriented Design, Model-View Controller, Data Access Layers, REST and the like.

Solve the Project Euler problems

Project Euler is a series of challenging mathematical/computer programming problems that will require more than just mathematical insights to solve. Although mathematics will help you arrive at elegant and efficient methods, the use of a computer and programming skills will be required to solve most problems.

The motivation for starting Project Euler, and its continuation, is to provide a platform for the inquiring mind to delve into unfamiliar areas and learn new concepts in a fun and recreational context.

Write code

I could have just said this.

Your opening paragraph tells me that you're confident in your abilities around algorithms and data structures. Your second paragraph tells me that you collapse under pressure in an unfamiliar environment. As such, I think you're asking the wrong question. It's not about improving your algorithmic thinking, it's about improving your comfort level in unfamiliar, high pressure environments. Being uncomfortable and nervous clouds your thoughts. Scatters your brain. Gives you writers block. Once you pass a certain point, personal frustration starts to set in and you start beating yourself. Once you get to that point, recovery is tremendously difficult.

Unfortunately, the trick here is definitely practice, practice, practice. The best practice you can get is by signing up for as many interviews as possible (best judging, high pressure, uncomfortable situation). Try a healthy mix of highly academic employers (i.e. Google, Amazon, etc) with startups looking for generalists. From my own experience, after interviewing with Google, everything else seemed like a breeze.

Also, as I'm sure you can tell from my post, I've dealt with the same exact problem on a few occasions myself (that is, deer-in-the-headlights). After going through a bunch of interviews (I wasn't even actually actively looking for employment at the time), I can tell you that I now feel much more comfortable in stressful situations where I'm being judged.

The most important thing to remember is that the person sitting across from you is just another (guy|girl). You can engage in peer-like conversation with them. You'll also likely find that once you start having two-way conversations, your comfort level will improve.

And, for the love of whatever you believe in... Talk through the problem. Don't just sit there staring at a whiteboard or screen. And ask questions.

I know this isn't a direct answer to your question. I think you're asking the wrong question.

For practice in the actual algo parts though, take a look at sites like projecteuler, interviewstreet, checkio (if you use Python), or any number of companies that offer challenges as part of their recruitment process (Facebook, Dropbox, etc).

It seems like your problem is not in understanding of how a particular algorithm works, but recognize the algorithm behind a question. Practicing algorithms only gets yourself familiar with the implementation. However, the implementation has less to do with recognizing an algorithm.

To me, recognizing algorithm belongs to a more generic thinking skill. My experience on this is nothing helps more than keeping an open mind and trying to look at things in different angle.