Foundations
How this course works
What the pieces are, how to move through them, and the one habit that decides whether any of this sticks.
What this is
This course teaches you to solve interview coding problems, using the 150 problems in the NeetCode 150 as its backbone. It is meant to be the only thing you need. There is no companion video, no separate problem list, no article you are supposed to go read.
You work top to bottom. Every problem arrives after the ideas it needs have already been taught and practiced, so when you hit it you should be able to make a real attempt. That is the whole design.
The pieces
Lessons mix a few kinds of block. Readings explain an idea. Drills make you use it immediately: predict what code prints, pick which version breaks, fill in how a stack evolves step by step, fix a bug, write a small function. Then there are the problems themselves, in the same workspace you would use anywhere else on CodeGround, with the same grader. Solving one here marks it solved everywhere.
Tip
Just go in order
You do not need to decide what to study, which problem to do next, or when to review. The order is the product. Old problems come back on their own, in end-of-unit retrieval lessons and in checkpoints, so you do not have to build a review system on the side.
Why it works
The habit that decides everything
When you get stuck on a problem, sit in it for a while before you reach for help. Twenty minutes of genuine stuckness teaches more than an hour of reading a solution you understood but did not produce.
There is a reason for that beyond discipline. Reading a solution creates a strong feeling of understanding and almost no ability to reproduce it. You will have met that feeling before, in a lecture that made perfect sense until the exam. The drills in this course exist to force the reproduction, not the recognition.
Help is available and you should use it when you are truly stuck, in this order: a nudge, then a hint, then an explanation, then the solution. The assistant will not hand you an answer before you have attempted the problem, and that is on purpose.
Python
Everything here is in Python. If you are coming from Java or C++, the next three lessons will get you to the point where the language stops being the thing slowing you down. If Python is already comfortable, skim them and do the drills anyway. They are short and they catch the specific gaps that cost people problems later.
Gotcha
Return, do not print
This trips up nearly everyone on their first graded problem. The small drills in a lesson print their results, because printing is how the drill shows you what happened. The real problems do not. They give you a function, and the grader calls that function and looks at what you return.
A function that prints the right answer and returns nothing returns None, and None is wrong no matter how correct the printed text looks.
Tip
Printing is still useful
Printing inside a solution is fine while you are working. It is how you see what a loop is doing when it misbehaves, and the workspace shows anything you print alongside the test results. Just make sure the answer leaves through return.
Check that the workspace runs
A one-line warm-up to confirm the Python runtime works in your browser. Make greet return the string Ready, then press Run tests. The first run downloads the Python runtime and can take a few seconds; later runs are instant.
Tests
print(greet())
Output
Run the tests when you are ready.