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Added random tests

Not StackOverflowException, just OverflowException ;)

[10,10] is the correct solution in that case

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Tests have evolved since

how did you passsed test?

Added

No random tests in JS

for input like [8,10,10,1] you'll get [10,10] instead of [8,10]

mutating array isn't

This can be solved in O(N) time & O(1) space.

no sample tests (JS)

I have basically no background in algorythm efficiency analysis so I don't focus on it ever so thank you for the explanation and suggestion; I would implement your solution using a .reduce() but it would equate to the same thing.

I imagine that there are more difficult kata where efficiency of the solution plays a part in success or not and I actually avoid those as it isn't something that I have ever needed to take into account.

If you were to use Array.sort(), first create a new array by doing array.slice(0), which will create a shallow copy of the input array. Then it can be sorted without mutating the input.

However, just using a simple for loop allows you to complete this Kata in O(n) instead of O(n log(n)); Using sort means that for large arrays you're going to see a huge performance disadvantage versus just finding the max and second max using a for loop.