Please clean up all the comments before pushing the changes and creating the PR.

Please clean up all the comments before pushing the changes and creating the PR.

Please clean up all the comments before pushing the changes and creating the PR.

Please clean up all the comments before pushing the changes and creating the PR.

Please clean up all the comments before pushing the changes and creating the PR.

Please declare variable names in English.

We are accessing this[i + 1] many times, hence we assign this to variable nextNum and use nextNum variable everywhere else. This will improve readability.

The <Int, Int> can be omitted since the compiler is smart enough to infer the generic type.

Also, there is an alternative way to declare a pair, and that is by using to infix extension function:
first to second

If we run your implementation for the input listOf(3, 1, 2), we would get the incorrect result Pair(3, 3).
Are the tests green for you?

nit: this.size -1 can be written as this.lastIndex

The test data for this method seems incomplete, and your implementation has a false positive in the tests, meaning the tests are green, but the actual implementation is incorrect.

In the above example for the input listOf(3, 1, 2) the expected output should be Pair(3, 2), and you implementation returns Pair(3, 3) which is incorrect. This is because the test didn't cover the case where the highest number in the list is at the first index.

I'm very sorry for the inconvenience with incomplete test data.

Please add a missing case to the test class and fix the bug in your implementation.

There is a mistake in the implementation where the lastIndex is stated. In the code you wrote, the lastIndex is the last index of the receiver object list. It's the same as if we wrote this.lastIndex.

TLDR: you should use it.lastIndex instead of this.lastIndex

In this case, the result will be correct, but if we, for example, filter elements of the list after sorting it, the lastIndex of the list we are operating on would change, and you would get an IndexOutOfBounds error.

Let's show this visually. In the following example, we have the list [3, 2, 4, 5, 1].
After calling sorted() on the list, we would get a new list [1, 2, 3, 4, 5], with the last index value being 4.
If after that, on the result list we call filter { it > 2 }, the new result list would be [3, 4, 5], where now the value of the last index is 2, and if we would call it[this.lastIndex] as in your code, we would get IndexOutOfBoundsException because this.lastIndex value is 4, which is greater than current last index.