suggested tags: combinatorics, permutations

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JS should be updated to Node 14.x and BigInt.

C++ Translation

The function name should be in snake_case in Python and Ruby.

Kotlin translation waiting for review

Something I did not find in the instruction is the possibility to find repeated words in the dictionary.
If you generate all possible permutations of a 'word' having repeated letters, you will generate a number of repetitions. For example:
starting from "eke" you will generate [('e', 'e', 'k'), ('e', 'e', 'k'), ('e', 'k', 'e'), ('e', 'k', 'e'), ('k', 'e', 'e'), ('k', 'e', 'e')],
which contains 2 copies each of 3 different words.
Is the solution you want the position of the given word in the full permutations list (in the example, both 2 and 3 would be correct),
or its position in the list of UNIQUE words, where the correct answer would be 1? (of course, numbers starting from 0)

This took me a really long time (almost the whole day) and I struggled a lot. I found the previous exercises in the series fairly simple but this one I really struggled with.
I plodded on, searching online for various things and I seemed to be progressing. I started by commenting out all but the first / simplest test, and worked to get that working. Once it did, I uncommented the next... now I have to deal with the iteration on creation... then I revealed the next one etc... that definitely made it more manageable... but then when submitting, I hit the createFilter tests... I swear, it simply wasn't clear to me how that was supposed to work at all. At this point I was guessing and it seemed like no combination of logic would get my tests to pass.
Eventually I did 'reveal solutions' which meant that I didn't get credit for completion, but I actually learned that I was super close and it was simpler than I thought.
I would have like to have seen the createFilter tests in the main Kata versus hidden until submission.

I got through, and I think I learned something about streams and conversions etc., but I have to be honest I don't think I'll retain what I took from creating the custom functions or predicate... They still seem obtuse to me and when I look at the code that was created as a result, it doesn't necessarily make sense to me why I'd use these.

Really enjoyed the series, thank you! This one was tough for me.

My Python solution fails with large input if I use reduce to compute the product of factorials, and works just fine if I use a for loop instead. Any idea why that happens?

@Azuaron, shall we use more specialized Predicate<Student> instead of Function<Student, Boolean>?

Why the type signture is different in exponential one?

Is it possible to implement one with type signature Cnum a -> Cnum a -> Cnum a?