Puzzlers on Kotlin Academy, week 1 - challenge your brain and Kotlin programming skills

Article originally published at blog.kotlin-academy.com

In last week, we’ve started publishing puzzlers on Kotlin Academy portal. Now we already have 3 of them. This is why we can show them here for you.

We will start from absolute classic of Kotlin puzzlers. Next we will check out more basic knowledge, and finally we will have original and more advanced puzzler that might surprise you. Have fun 

Scala-like functions

fun hello() = {
    println("Hello, World")
}

hello()

What will it display? Some possibilities:
a. Does not compile
b. Prints “Hello, World”
c. Nothing
d. Something else

Answer is not so simple, but to see it, you need to check out this link or end of this article, since we don’t want to spoil it.

Indent trimming

val world = "multiline world"
println("""
    Hello
    \$world
""".trimIndent()

What does it display? Some possibilities:
a)

Hello
$world

b)

    Hello
    $world

c)

Hello
\multiline world

d) Doesn’t compile

Author: Dmitry Kandalov

If you know trimIndent and triple quoted strings, then the answer should be clear. Until you don’t know it well enough  If you are not sure, check out answer here of at the end of this article.

If-else chaining

fun printNumberSign(num: Int) {
    if (num < 0) {
         "negative"
    } else if (num > 0) {
         "positive"
    } else {
         "zero"
    }.let { print(it) }
}

printNumberSign(-2)
print(",")
printNumberSign(0)
print(",")
printNumberSign(2)

What does it display? Some possibilities:
a) negative,zero,positive
b) negative,zero,
c) negative,,positive
d) ,zero,positive

Author: Kevin Most

This one is tricky, so think twice. When you are ready, check answer here or below.

Answers and explanations

For “Scala-like functions” correct answer is:

c. Nothing

Why? Here is an explanation:

hello is a function that returns function created using lambda expression. It’s just returning function. To print text, we need to invoke it: hello()() // Prints: Hello, World

For “Indent trimming” correct answer is:

c)

Hello
\multiline world

Why? Here is an explanation:

A raw string is delimited by a triple quote (”””), contains no escaping and can contain newlines and any other characters. Although dollar cannot be used there even with escape character . If we want to use $, then we need to use {‘’} instead

For “If-else chaining” correct answer is:

d) ,zero,positive

Why? Here is an explanation:

Remember that the else if construct is really just calling else with a “single-line” if, which is the rest of your expression. In Kotlin, functions are resolved before if-else blocks, so the .let { print(it) } is only applying to the final else if. So in this case, the result of the first if statement will not be used and the function will return immediately. To avoid this situation, you can wrap the entire if … else … in parenthesis, and then chain .let on it

Do you want more puzzlers in the future? Track Kotlin Academy portal or subscribe to our mailing list.

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