Challenge 1: when as an Expression — Solution

fun seasonFor(month: Int): String = when (month) {
    12, 1, 2 -> "Winter"
    3, 4, 5 -> "Spring"
    6, 7, 8 -> "Summer"
    9, 10, 11 -> "Autumn"
    else -> "Invalid month"
}

fun main() {
    println(seasonFor(1))
    println(seasonFor(7))
    println(seasonFor(10))
    println(seasonFor(13))
}

/*
Output:
Winter
Summer
Autumn
Invalid month

Notes:
- seasonFor is a single-expression function; its entire body is the when
  expression, so its result is returned directly with no "return" keyword.
- Each branch groups multiple month numbers with a comma (12, 1, 2 -> ...)
  rather than needing three separate branches with identical results.
- else covers any value outside 1-12, keeping the when exhaustive for all
  possible Int inputs.
*/