Here are some resources on coding interview patterns:
- https://www.educative.io/courses/grokking-the-coding-interview (PAID)
Here are some additional resources for data structures and algorithms practice:
- Firecode.io I have only used this for a few days but it is amazing! It has a very user-friendly interface and it is also designed to provide spaced-repetition of problems to enhance learning and memorization.
- Pramp was introduced to me by Infinitely Finite and is also highly recommended in Mohsin Ali’s guide. Pramp provides free interview practice with other developers. Pramp has helped me improve at solving problems, explaining my thinking process, and teaching and helping others improve their algorithmic coding.
- Geeks for Geeks Practice is great because problems can be sorted by company, topic, and difficulty. There are countless problems and there are plenty of explanations as well. I have fun solving problems here and improving my ranking 🙂
- Tushar Roy‘s video explanations are very organized and easy to understand. He breaks down concepts step-by-step and also draws out every step, and then shows how to implement the concepts as code.
- Hacker Rank has problems from Cracking the Coding Interview along with superb video explanations by author Gayle Laakmann Mcdowell.
- A2 Online Judge has an endless supply of practice problems organized by category.
Here are some of lessons I have learned over the last few weeks solving problems at LeetCode, Geeks for Geeks, Pramp, and Hacker Rank.
- Solving code challenges is fun! I love seeing the Green Check Mark or the PASS or earning points 🙂
- Code challenges are very difficult. They can be very frustrating and upsetting. But the reward is learning the concept. Learning a concept, i.e. recursion, is like earning a key that opens up doors to both solving similar problems and to being able to understand more complex concepts (i.e. backtracking).
- I used to just try to start coding by trial and error. That was a disaster. I have learned to really focus on using examples. I try to have a number of input and output examples including edge cases, smaller examples, and medium size examples.
- After I have my examples, I need to be able to solve it in plain English first. I like to draw things out, i.e. the array with values, linked lists, trees, etc. Then I try to solve these examples in plain English.
- If I have tested my plain English logic and things seem to work, then I will finally start to code. If my logic does not seem to work, I will start brainstorming possible solutions.
- If at any point I get stuck, I will go for a walk or stretch.
- The most important thing about the code challenges is that I am having fun doing them. As long as I keep on having fun, I will keep learning and improving my skills.
- This is a great soundtrack to listen to while coding Crypt of the NecroDancer OST.
- Everyone learns and improves at a different pace depending on their experience, natural aptitude, time and energy, etc. I have learned that I feel much better when I compare myself to my past self (and see how much I have improved) and to my future self (to see where I want to be), instead of comparing myself to others.
- Instead of thinking, “I can’t solve this problem, I have never seen anything like this before :(” I am better off thinking, “Great, I now have the opportunity to learn something new :)”
The code challenges have tested my patience at times, but overall it has been great. I have learned and improved so much, I can’t wait to solve even more and bigger problems 🙂
Before I was doing the LeetCode algorithm problems in order of difficulty. I was doing and redoing the problems in random topic order.
I am now doing the problems by category. I am not finishing the category until I am able to solve the problems in the category. I think this is an improvement because it is more drilling and practicing of recalling and typing the correct solution. It is definitely more difficult than just searching for patterns, but it is providing me with a better understanding of what each line of code does in a solution.
I have recently begun to do code challenges from TopCoder.
I first heard of TopCoder from John Sonmez here: So You Want to Become a Better Programmer? (TopCoder).
I started by doing the archived problems here. The problems are sorted by the percent of competitors who were able to solve them–basically in order of difficulty.
The questions can be fun but a few of them are impossible for me to understand and the interface requires a very large monitor for me to see everything. But overall it has benefited me because I get to attempt to understand a requirement, pass tests, then look at successful and cleanly written code from past competitors.
Check out this great post by Joanna Chen: How I landed a Google internship in 6 months
She has has great advice on building, practicing coding problems (Pramp.com), meeting people, applying, etc.
Special thanks to Siddharth for being the first to introduce me to Pramp.com for free interview practice.
Here are the sites I have experience with and my thoughts
- LeetCode is excellent because there are many problems and explanations. Furthermore the problems without explanations have answers and commented solutions in the discussion boards. It is the best online judge in my (limited) experience.
- Cracking the Coding Interview has many questions and detailed answers in Java.
- Data Structures and Algorithms Made Easy in Java is excellent. Sure there are many, many, many typos. But it has so many code samples for each of the data structures, explanations from worse (brute force) to best (optimized) along with advantages and disadvantages of the many possible solutions.
An honorable mention goes to Free Code Camp. The first time I ever had fun solving code challenges was at Free Code Camp. They did an amazing job of starting off with relatively easy challenges, then they raised the bar. Before I knew it I was doing difficult challenges, yet the hours flew by.