I had something like this:

    var heights: Array< Pair<Int, Int> > = ... //populating the array
    heights.sortBy { it.second };

It was not obvious at all that I had to use curly braces. The documentation says:

    inline fun <T, R : Comparable<R>> MutableList<T>.sortBy(
    crossinline selector: (T) -> R?) (source)

This is after I figured out that I'm not supposed to use sortWith (I never figured out how to use this one)

The curly braces are the syntax for lambdas, one of the basic types `(T) -> R?`. There are plenty of examples for using that, but in the respective chapters: https://kotlinlang.org/docs/reference/lambdas.html#higher-or... or in this bunch of examples: https://kotlinlang.org/docs/reference/idioms.html#filtering-...

The docs are arranged in a way that one reads them in the order they are written (at least the first half). I supposed that would take more than half an hour given at the competition.

I don't think Kotlin is the best choice for programming challenges like codeforces - they really don't let him shine (although I use it whenever I can). But if this is a valid case, we can collaborate and write a short tutorial for C/C++ to Kotlin programmers.

Oops, copied the wrong snippet out of the two:

    inline fun <T, R : Comparable<R>> Array<out T>.sortBy(
    crossinline selector: (T) -> R?) (source)