Grokking Coding Interviews with 99 essential problems

A big reason my brother Naeem and I started Educative was to help software engineers like ourselves prepare for technical interviews.

As someone who has participated in hundreds of software engineering interviews (on both sides of the table), I will be the first to admit that coding interview prep can be one of the most stressful aspects of software engineering.

To stay competitive in an interview setting, we're expected to stay knowledgeable and up-to-date on everything from university-level data structures and algorithms to new frameworks and tools much of which may not even be directly applicable to our day-to-day work.

It goes without saying that the stakes are very high. Failing a coding interview in a competitive job market can mean missing out on a key career move and losing tens of thousands of dollars in total compensation.

However, when it's time to look for a job whether it's your first new role in a few years, or your first in the industry its typically very time-consuming to get interview-ready. When youre already working a full-time job, or have life obligations, it can be very hard to find the necessary time to prepare fully.

That means efficient interview prep matters, now more than ever.

So, we partnered with hiring managers at top tech companies to formulate an essential list of 99 coding interview challenges. The goal is to provide comprehensive prep in far less time than traditional methods.

Today I want to share why I think Educative-99 is such a useful resource, and discuss the methodology behind how we selected the problems. Then I will share some tips for how you can get the most out of Educative-99 to optimize your interview prep time.

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A streamlined approach to LeetCode-style prep

Back when I was preparing for my Facebook interview, I remember LeetCode being the industry favorite for interview prep. I still think it can be a helpful tool, but there is a big problem that has emerged with LeetCode in recent years.

It actually has to do with the sheer number of problems on the platform.

When I first learned about LeetCode in the early 2010s, it had around 200 problems. Now, that number has grown to almost 3,000. At face value, it may seem like more problems is a good thing and in a sense it is. But whats happening behind the scenes is that LeetCode is in an arms race with tech companies. Companies are adding new coding challenges to their interview loops all the time in order to stay ahead of platforms like LeetCode while LeetCode is constantly adding new problems in the attempt to account for any coding question a company could ask.

The result is an insurmountable crush of problems with a lot of redundancy and not much structure.

To put it another way, LeetCode's greatest strength has become its greatest weakness. Back in 2011, it was possible to finish LeetCode, and feel like you prepared comprehensively. Those days are long gone. The sheer number of problems create a system that is no longer a scalable, or digestible, approach to interview prep. Approaching LeetCode with the goal of solving every potential problem you might encounter (or worse yet, memorizing solutions) is not a successful prep strategy.

The key to comprehensive coding interview prep isnt to drill as many problems as possible. Rather, its about being strategic and efficient with the problems you do study.

You can achieve this result by focusing on essential coding interview patterns.

The reality is that those 3,000 problems on LeetCode aren't really 3,000 unique problems. In fact, the overwhelming majority of those 3,000 problems and by extension, most of the possible questions that a company might ask can be broken down into just two dozen common coding patterns.

Our brains are already wired to identify patterns. As software developers, we are especially good at this. So if you can quickly identify the defining characteristics of a problem, you're already well on your way to solving it.

This pattern-based approach to coding interview prep is how the best engineers I know prepare for interviews. Educative-99 was developed to help you learn and practice that same successful strategy.

Comprehensive coding interview prep... in just 99 questions

Educative-99 is our most streamlined coding interview prep resource.

Working alongside hiring managers at top tech companies, we identified 26 comprehensive patterns that can be used to solve almost any coding interview problem. Educative-99 then whittles down the to-do list to just 99 hand-selected problems of varying difficulty levels. Each problem represents one of the 26 patterns. By working through each problem, you'll master each pattern, and ultimately, be more confident in the hot seat.

Our mission was to demystify coding interview prep so that developers can spend their time practicing the problem-solving muscle memory that will actually help them ace an interview.

Why coding interview patterns matter

By memorizing, learning, and applying these patterns you can confidently nail coding interview questions.

Here are just a few of the 26 essential coding interview patterns you will practice and learn to identify through Educative-99:

• Two Pointers
• Sliding Window
• In-place Reversal of a Linked List
• K-way Merge
• Dynamic Programming
• Matrices
• Tree Depth First Search
• Hash Maps

With easier questions, you should be able to quickly hone in on the right pattern and use that muscle memory to come up with a solution.

On the more complex questions, you should be able to identify two or three possible patterns, and then work through your thought process of applying these solutions to the specifics of the question.

Tips for how to get the most out of Educative-99

Not everybody has weeks to devote to interview prep, especially if you're working a full-time job. So, I'll share a few tips that will help you get interview-ready with Educative-99 even more efficiently.

1) Start with medium difficulty questions

If you start in the middle of the difficulty range you can easily work your way up or down depending on your confidence in each pattern.

If you can solve a medium difficulty question easily there's no need to waste time practicing its easier counterparts. Just keep in mind that not all difficulty levels are equal across patterns. For example, a medium-level cyclic sort problem is probably going to be harder than a medium-level two pointers problem.

2) Don't look at the solution

I know it can be tempting to check the solution if you can't figure it out, but try to avoid this. Instead, go back and try an easier version of the problem first. Then, revisit the question when you feel more comfortable with the pattern.

Memorizing the answers to individual questions won't help you but internalizing each pattern will.

3) Do the hard questions in a random order

Once you're feeling confident with each pattern, do the hard questions in a random order to simulate a real interview environment.

Hard questions can often fall in between patterns, and you'll have to choose two or three possible approaches. There's a good chance you'll receive a problem like this in an interview setting (especially if you're applying for a more senior position), so getting sufficient practice with ambiguous problems is invaluable.

One more reminder: being confused during your preparation is a good thing! This is how you train yourself to puzzle through a problem and find the optimal pattern to apply. It's best to be as comfortable as possible with this method because it's likely that your interviewer will want to hear your thought process, too.

Practice with the help of your own AI coding interview coach

One last feature to note: Educative-99 is now available with our built-in AI coaching model. That means you can get real-time feedback on every line of code you type.

Educatives AI assistant is capable of identifying errors, suggesting improvements, and running complexity analysis, so you can learn how to improve your problem solving skills all in one place.

Just look for the Powered By AI button in our coding widgets to get started.

Currently, we offer Educative-99 in the following languages (with more on the way soon):

• Educative-99: Python
• Educative-99: JavaScript
• Educative-99: C++
• Educative-99: Java
• Educative-99: Go

Educative-99 is our one-stop resource for efficient coding interview prep. However, if you want to spend more time with the 26 essential coding interview patterns, I highly recommend these hands-on courses as a primer:

• Grokking Coding Interview Patterns in Python
• Grokking Coding Interview Patterns in JavaScript
• Grokking Coding Interview Patterns in C++
• Grokking Coding Interview Patterns in Java
• Grokking Coding Interview Patterns in Go

Happy learning and good luck with your interviews!

Fahim ul Haq
CEO & Cofounder
educative.io