how do you test for time?

great solution bro

You can declare a variable "size" for keeping the word's length.
Using the length() method in a loop may be quite a drag for your pc.

i agree. it kind of kills the point of this kata

Would be a lot better to use StringBuilder, that thing is no joke 100 times faster

No, time complexity is still O(n * (n + n + n)) = O(n²).

Concatenating strings with += in a loop can have a time complexity of O(n^2)!!!!
Adding this all together, the overall time complexity is O(n^3).

It has to be one or the other, since all the other values are equal to each other.

I run your in 600+ ms and mine in 260 ms.
I test every value until I find the unique where you sort the whole array.

@kjanus-thecreator Description says. "The tests contain some very huge arrays, so think about performance"
I insist this 6 kyu kata's solution should be implemented in imperative style, not two-lines declarative one. Otherwise it must be 7 kyu.

Isn't this inefficient for large arrays?

it's soo fucking clever man, nice one !

This is not an optimal solution, neither space nor time wise. It's not necessary to sort the arrays or even create any sort of counter list / hash. Instead, its possible to do it with four variables, two to store the different numbers and two to store the counts. A more efficient solution only needs a single O(n) traversal of the entire array at worst, as well as O(1) extra space. Dunno why this is so upvoted but to each their own I guess.