Create mentoring.md for grains exercice in cpp #2339
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Creating the guide for the solution of the grains exercise in cpp. Offering an imperative and a recursive solution for the first function and explaining how to do correctly the second function.
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All three functions in this document are implemented with loops or recursion.
That is a valid way to solve the exercise.
But there's a more direct way by calculating the result.
square() can be implemented with 1ULL << (indice - 1) and
total() can be implemented in a variety of ways, e.g.:
return 18'446'744'073'709'551'615;
return 0xFFFF'FFFF'FFFF'FFFF;
return (1ULL << 63) * 2 - 1;
return (1ULL << 32 << 32) - 1;
return (2ULL << 63) - 1;
return UINT64_MAX;
return std::numeric_limits<std::uint64_t>::max();
return ~static_cast<std::uint64_t>(0);
return static_cast<std::uint64_t>(-1);
return std::bitset<64>().set().to_ullong();
return 2 * square(64) - 1;I'd guess that this direct calculation of the result was one of the ideas behind the exercise. Do you mind including such a direct calculation as well for the two functions?
| return result; | ||
| } | ||
| ``` | ||
| A cleaner way to do this is to use a recursive function : |
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I'd argue that it is subjective whether a recursive implementation is "cleaner" than one using a loop.
Personally I prefer the function with the loop, with my imperative mindset I find it a tiny bit easier to understand, and it avoids the overhead of the recursive function call.
If you really want to call it "cleaner" I'd prefer if you make it clear that this is an opinion (like later with the "in my mind".)
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| The first way to implement this function is to use a for loop : | ||
| ```cpp | ||
| unsigned long long square(int indice) { |
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Here and later: "indice" sounds like French or Italian, right? Since everything else is in English how about index?
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Yes I'm french, it happens sometimes that I let a french word in my code. I will do this changes thx :)
Changing indice to index Removing "cleaner" for the recursive method Adding the direct method for the first function
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I've removed "cleaner", changed "indice" to "index" and added the direct method. Hope you will like the changes, don't hesitate to ask me for more changes if you need. |
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Thank you! The whole documents sounds like its target audience are "students", e.g. it explains bitwise left-shifting with an example. But these mentoring notes are for "mentors" who (ideally) should already have solved the exercise, understand the assignment and solutions, and want to help others improve their solutions. Mentoring notes typically contain (1) reasonable solutions, (2) common issues that often occur in solutions (i.e. subtle errors or code smells that a mentor might want to look out for), (3) common suggestions that often can improve solutions, and (4) talking points that repeatedly come up in these discussions. (see https://exercism.org/docs/building/product/mentoring-notes) For example: I've seen many solutions that implement both functions by calling If you want to explain the exercise to a "student" you might want to write "approaches" instead. (see https://exercism.org/docs/building/tracks/approaches). Typically they explain language constructs like the operator
Do you mind adding an implementation with a direct computation for the second function, too? And a few tiny nitpicks:
We love contributions, especially documentation. If you need any feedback, input, or help feel free to reach out to me or @vaeng on the forum or on Discord. |
removing space before colon adding a direct implementation for total adding common issues and suggestions section
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I've done the changes you've asked for. I wasn't sure about the direct implementation because I often see direct implementation with ULLONG_MAX however it's, in my opinion, like cheating and hard coding the solution just a bit cleaner. So, with this point of view, I also add it to the common issues. |
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@IsaacG Thanks for reminding me. This got lost in my inbox. I have to admit I'm unsure about this. Do we really want to encourage students to solve this exercise naively, with loops that repeatedly multiply and/or add? Sure, such a solution is not objectively wrong, but in my opinion it does not go beyond translating the instructions directly into C++, there's no discovery or learning experience. IMHO this exercise aims at a more elaborate or efficient approach, it wants the students to discover the underlying mathematical principles and that the number of grains on a square and on the whole board can be calculated directly, either with exponentiation or with bitwise operations. IIRC back in Exercism-v2 when exercises had tags this was tagged with "bit operations". I'd appreciate if some of the other experienced mentors or maintainers would weigh in. |
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I would also go for the "bit" direction as it is the most straightforward way to solve an exercise based on 2^x questions. I might be heavily biased though, as I am wired to binary and haven't been a novice student in a while. |
I don't think we want to encourage students to solve things in any particular direction. We want to encourage them to write code, think and explore. The loop approach isn't ideal but it's not wrong. It's good practice either way. I would encourage students to examine the numbers and look for patterns and think about ways to leverage them.
Exercism is about programming, not math and finding closed formula solutions for problems. I've seen people solve sum-of-multiples and multiples-of-sums using closed forumulas but I certainly would not expect that of most students. Unless the instructions explicitly call out that students should look for bitwise approaches, I wouldn't push for that very much. On the Python track, I never suggest replacing exponents with bitwise shifts. |
Are you sure about that? I've seen quite a few mentoring notes that said something like "try to nudge the student towards this ..." or "suggest that they ..." or "direct them towards ...".
So you do want to guide them towards a less naive solution? I'm with you on that.
As I wrote earlier, IMHO exponentiation is fine, too. (But in C++ you have to be careful when using |
I'm sure that's what I think. That doesn't mean all the mentoring notes align with what I think we want.
Yes. I want to guide them to explore and think about less naive solutions. Without being prescriptive and telling them they need to implement any specific solution. If they recognize the pattern and opt not to use it in their solution, I think that's entirely fine. |
Creating the guide for the solution of the grains exercise in cpp. Offering an imperative and a recursive solution for the first function and explaining how to do correctly the second function.