Approximate Pi from randomly generated integers

Pi_coPrime.kt

import com.google.common.math.IntMath
import java.lang.Math.sqrt
import kotlin.random.Random.Default.nextInt
import kotlin.system.measureTimeMillis


/**
 * Approximate Pi from randomly generated integers given that Pr( coPrime(n,m)  ) = 6 / ( pi^2 ).
 * Guava's implementation of GCD is about twice as fast as the "naive" one.
 */

fun Pair<Int, Int>.gcd(): Int =
        when (second) {
            0 -> first
            else -> Pair(second, first % second).gcd()
        }

fun Pair<Int, Int>.gcdG() = IntMath.gcd(first, second)


fun main(args: Array<String>) {
    val sample = 10_000_000

    val duration = measureTimeMillis {
        val copCount = generateSequence { nextInt(2, 10_000) }.take(sample)
                .zipWithNext()
                .map { it.gcdG() }
                .filter { it == 1 }.count()

        val prob = copCount / (sample - 1).toDouble()
        println(sqrt(6 / prob)) // 3.1414253391426907
    }
    println("In $duration msec.") // In 1046 msec
}