Updated: Feb 2, 2025 Author: Navdeep Singh
You should be comfortable programming in at least one common language. This means you know the basic syntax, like loops, conditionals and functions.
I recommend using the Python language for coding interviews. It's readable, has good error messages and is easy to learn. I personally learned Python only for coding interviews and it only took a few hours to learn the basics.
Java and C++ are also good choices. Other common languages like JavaScript and Golang are also fine, but they have less built-in libraries and data structures.
In a real interview, if your programming language does not have a built-in data structure that you need, your interviewer will let you define your own interface / API for it. You probably won't have to actually implement it from scratch, unless that's part of the problem.
If you're interested in learning Python, you may find these courses on NeetCode helpful:
- Python for Beginners - Learn the basics of Python with 80 interactive coding challenges.
- Python for Coding Interviews - Learn how to use all of the built-in data structures and algorithms in Python.
- Python for Object-Oriented Programming - Learn how to write object-oriented code in Python.
You should be familiar with the most common data structures and algorithms. This includes:
- Knowing the time and space complexity of each.
- Knowing how to implement them.
- Most importantly, knowing how to use them in your programming language of choice.
Here are the most common data structures in no particular order:
- Dynamic Arrays
- Linked Lists
- Stacks (Usually implemented with a dynamic array)
- Queues
- Binary Trees
- Hash Maps / Sets
- Heaps
- Graphs
Here are the most common algorithms in no particular order:
- Binary Search
- Binary Tree Traversals
- Sorting (Merge Sort or Quick Sort)
- Breadth-First Search (BFS)
- Depth-First Search (DFS)
You don't need to be familiar with all of these topics, but these are almost guaranteed to come up in coding interviews. Many colleges will touch on these topics, but coding interviews will require you to be intimately familiar with them.
You may find these resources on NeetCode helpful for learning these topics:
- Data Structures and Algorithms for Beginners course on NeetCode
- Practice Problems to implement common data structures and algorithms from scratch.
There are many more advanced concepts and math topics that can come up in more difficult coding interviews. These include:
- Dynamic Programming
- Complex Graph Algorithms
- Segment Trees
Many hard problems will require you to know one or more of these concepts. Without them, you will have little chance of solving these problems on your own.
These concepts take time and practice to learn. I recommend learning these concepts as you go. Learn them when you actually encounter them in practice problems, otherwise you will probably forget them anyway.
Unless you're a competitive programmer willing to dedicate thousands of hours to practicing, it's impossible to know every advanced topic in-depth. Try to prioritize the more common & easier topics before moving to the more difficult ones.
You may find these resources on NeetCode helpful for learning advanced topics:
- Advanced Algorithms course on NeetCode
- Practice Problems to implement common advanced algorithms from scratch.
Just get started and don't overthink it. Find a reasonable list of problems and start solving them.
Solve the first problem in the NeetCode 150 or NeetCode 250 list. And then keep going and never look back.
Both of these lists are comprehensive and provide a good mix of easy and hard problems.
You probably want to plan out the best way to study. That's reasonable. But don't overthink it. So many people spend more time thinking about the best way to study than actually studying.
Just get started. What's the worst that can happen? Maybe you attempt a problem that's too difficult. That's fine. You can always come back to it later.
Many people are discouraged when they can't solve a problem.
But consider this: Many of these problems were first solved by professional mathematicians in the past. You're not expected to easily figure these out on your own.
Each problem on NeetCode has a video solution and code solutions in several languages. Take advantage of them. It's not "cheating" to look at the solution. As long as you can understand the solution, you're doing great.
Do not:
- Copy and paste the solution.
- Spend several hours trying to solve a problem you're stuck on.
- Blindly memorize algorithms without understanding why they work.
Do:
- Attempt the problem on your own.
- Try drawing out the problem on paper.
- Look at the solution if you're not making progress after 15 - 20 minutes.
- If you can't understand the solution within 45 - 60 minutes, try an easier problem.
- Revisit problems that were challenging for you, resolve them from scratch.
Tip: The difficulty of some problems is not accurate. Often, there are "medium" problems that are actually more difficult than "hard" problems. Don't focus too much on the difficulty rating, just try to learn the algorithms.
You probably want to maximize your chances of passing the interview, right? So how do you decide when you are done preparing and ready for the interview?
That's the thing. Technically you're never done preparing. You will never have a 100% chance of passing any given interview. Think of it more as a game of probability or a distribution.
You might prepare enough that you can pass 50% of interviews, or 90% of interviews, but never 100%.
A good rule of thumb is if you can solve most medium problems that you haven't seen before, within 20 to 25 minutes, you can probably pass most interviews.
If you have limited time, here are the most important topics to focus on:
- Arrays
- Hash Maps
- Trees
- Graphs
The hard thing about these topics is that they are very open-ended. For example, arrays are simple, yet there are hundreds of algorithms that can be performed on them, like binary search or sliding window.
Graphs are even more complex. Some problems may require a simple DFS, but others may require a complex algorithm like Dijkstra's or a topological sort.
To solve this problem, I created the NeetCode 150 and NeetCode 250 lists. These lists touch upon the vast majority of the topics you will see in coding interviews. They are ordered in a way that each problem builds on the previous ones.
You don't need to solve every problem in them, but the more you practice the higher your chances. If you're in a rush, you should prioritize the easy and medium problems in these lists.