Your posting is already 13 hours old but I hope you still see this message :)<p>First of all, being sometimes involved in teaching CS to people, I like your website. You have obviously spent a lot of time on the question of how to teach people programming (the latter in the sense of "How to write a program that solves a given problem?"). I have seen textbook authors with less dedication.<p>However (there is always a "however" or "but"), I am wondering whether you are using the right approach for the N Queens problem. You are following a bottom-up approach. For example, on the first page you let people write a helper function "validateQueenPlacement", followed by another helper function "nextRowColumns" on page 2. For somebody who doesn't know the complete solution, it's very hard to see why you would need those two functions. Of course, <i>you</i> know that you will need them but you have already seen the final solution!<p>You are probably familar with the top-down approach by Wirth (1971) called Stepwise Refinement. I think (but I cannot prove it) that most CS educators see Stepwise Refinement as the superior approach because it encourages people to think about the problem and not the code. Why don't you let the reader write first the high-level (pseudo-)code for the backtracking:<p><pre><code> http://sunnyday.mit.edu/16.355/wirth-refinement.html#3
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Once the reader has written the code for the highest layer, it becomes obvious what the helper functions should be, what their parameters are, and what data structures are needed. I know that Stepwise Refinement is unpopular nowadays because it forms a kind of psychological hurdle (bottom-up gives you <i>directly</i> small functions that you can unit-test) but I think it really helps people to guide <i>themselves</i> to the solution.
Feels very weird to me to spend time and energy building tools for a type of interview process that is becoming more and more derided by the community?
For me, completing the Spiral Matrix, I did not find the hint for the third and final section relate-able at all to my solution.<p>Essentially, it assumes a bit too much the shape of the resulting solution.<p>That's not to say I didn't get value from the hint, or that I think others will not - on the contrary, it is a valuable and clear hint.<p>The unfortunate part is just the feeling of being taken completely "out of it" in solving the solution with a slightly different approach and wondering momentarily if somehow one is wrong, even though one is passing all the tests.<p>The recap is also fairly lacking in content, but I imagine that is clear to you already.<p>Nice job on the site, generally.
I only had a couple hiccups with submissions and some weird aliasing on the editor if I would edit a line before it redrew.<p>Edit: add some dropped words