Triangle Exercise: Instructions and Proposed Solution

Exercism
1

I recently saw Triangle exercise formulation and proposed solution and there are few things I am not sure about.

First, in the exercise instructions it says we should check that a <= b + c. I think it should be < instead of <= as you cannot make a triangle when one side is equal to the sum of the other two.

As for the proposed solution, there are few remarks that I would like to make. is_valid is implemented in the following way.

def is_valid(sides):
    if not sides[0]:
        return False
    return all(side * 2 < sum(sides) for side in sides)

The condition not sides[0] will work only if sides are sorted; e.g. it won’t work for [1, 0, 0] . Also, none of the tests covers cases like this.
Here, sum(sides) is used in the generator. Is sum being evaluated in every iteration (making it quadratic complexity; here it is not important as sides has length 3, but I would prefer avoiding stuff like this in proposed solutions) or Python optimises this “under the hood”?
I believe it would be better idea to store sum(sides) in a variable and then use it in the generator.

Another thing I was not sure about is the proposed implementation of equilateral.

def equilateral(sides):
    return is_valid(sides) and len(set(sides)) == 1

Does it really make sense to check if triangle is valid here? Isn’t it sufficient to check if all the sides have the same length greater than zero?

def equilateral(sides):
    return len(set(sides)) == 1 and sides[0] > 0
2

Would you mind linking to which solution/code you’re referencing? Is this a specific community solution? Community solutions aren’t always perfect or optimal. Are you asking how the code works? If that person’s solution could be better?

3

This was a proposed solution that was shown to me while I was mentoring a student.
Here are the instructions

I cannot find the proposed (or exemplary solution). It could be that someone updated it in the meantime.

4

It’s hard to comment on potential changes to something without seeing where/what that something is :slight_smile:

Are you wondering about that specific solution? Asking for details/clarification about how it works? Proposing that something somewhere be changed?

5

This is what I see under the Guidance tab.

Screenshot 2023-09-27 at 20.23.05
Screenshot 2023-09-27 at 20.23.051178Ă—1128 135 KB

6

It’s hard to comment on potential changes to something without seeing where/what that something is :slight_smile:

Are you wondering about that specific solution? Asking for details/clarification about how it works? Proposing that something somewhere be changed?

I literally made a suggestion about replacing <= with < in the instructions. The link to the instructions is in my first response.

I cannot find the link to the “reasonable solution” on GitHub, otherwise I would have posted it.

7

That’s the mentor notes for the exercise.

Those are notes and not intended to be the “optimal” solution. The notes explicitly say this is a “reasonable” solution – not an optimized solution. You can suggest improvements to those notes via a PR to the linked file.

You can propose changing the problem spec via a forum discussion about that specific part of the exercise (vs the mentor notes). But be sure to first read Chesterton's Fence | Exercism's Docs and Suggesting Exercise Improvements | Exercism's Docs

In terms of runtime, the two are extremely close. I personally prefer to optimize for readable code here :slight_smile: Either is reasonable, though.

Either is reasonable. I like this approach because it is consistent with how the other cases are treated.

8

I see, thanks!

Sorry for the confusion, so far I only suggested changes via GitHub issues. This is the first time I am doing it via forum.

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