64. Random

kotlin.random.Random is the multiplatform random generator. Seeding it with Random(seed) makes the sequence reproducible — every run with the same seed produces the same values, which is exactly what we want for a deterministic example (and for tests).

import kotlin.random.Random

fun main() {
    val rng = Random(42)

    println(rng.nextInt(100))        // 0 until 100
    println(rng.nextInt(10, 20))     // 10 until 20
    println(rng.nextDouble())        // 0.0 until 1.0

    val colors = listOf("red", "green", "blue", "yellow")
    println(colors.random(rng))      // pick one element
    println(colors.shuffled(rng))    // a new shuffled list
}

The collection helpers random and shuffled accept a Random instance, so they share the same seeded stream. Call them with no argument to use the global Random.Default, which is not reproducible.

Running it:

$ kotlin run
33
10
0.9049568172356872
green
[yellow, blue, green, red]

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