Kotlin loop with irregular steps

Question

I have been trying to translate a Java for expression into Kotlin which produces this sequence:

1,2,4,8,16,32,64

This is the Java code:

for(int i = 1; i < 100; i = i + i) {
    System.out.printf("%d,", i);
}

The only way I have found to translate this into Kotlin is:

var i = 1
while (i < 100) {
    print("$i,")
    i += i
}

I have tried to use step expressions, but this does not seem to work. Is there any way to express this type of sequence more elegantly in Kotlin?

I know you can have code like this one using Kotlin + Java 9:

Stream.iterate(1, { it <= 100 }) { it!! + it }.forEach { print("$it,") }

But this relies on Java libraries and I would prefer Kotlin native libraries.

Kiskae · Accepted Answer · 2017-09-24 00:29:06Z

7

You can use the generateSequence function to create an infinite sequence, then use takeWhile to limit it at a specific value and then use forEach instead of a for-in construct to handle each iteration:

generateSequence(1) { it + it }.takeWhile { it < 100 }.forEach { print("$it,") }

edited Sep 24, 2017 at 0:29

answered Sep 23, 2017 at 21:20

Kiskae

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