If you’re an outlier, I’m out there with you: I’ve also been writing software professionally for 20 years, I have no CS degree, and I’m not fool enough to reimplement algorithms like quicksort that are sitting right there in stdlib. I similarly found this explanation a lot more useful than anything else I have read about quicksort, and I’m confident I could implement it now, but couldn’t have before I read this.
If you guys like visual-explanations that are a bit more intuitive -- I put actually made guides on both data-structures and algorithms not too long ago which you can find here:
The visual is extremely hard to understand how it relates to the description, given that it looks to be 1-indexed, but the description only makes sense for 0-indexing (4th element stores the sum of the first 4 elements), not to mention none of the binary indexes seem to be storing the correct sums (or they're storing sums of a tree that isn't being presented).
The visual is directly from here (I recommend you give it a read if you want to grasp the full intuition on how a Fenwick tree works (page 97)): https://cses.fi/book/book.pdf
I should have included the full visuals which are included there and I can see your point on why people would get confused by that visual - so I'll make a note to include the full image when I have more time. Thank you for the feedback.
