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Permutations by swapping: Difference between revisions
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=={{header|Scala}}==
<lang Scala>object JohnsonTrotter extends App {
private def perm(n: Int): Unit = {
val p = new Array[Int](n) // permutation
val pi = new Array[Int](n) // inverse permutation
val dir = new Array[Int](n) // direction = +1 or -1
def perm(n: Int, p: Array[Int], pi: Array[Int], dir: Array[Int]): Unit = {
if (n >= p.length) for (aP <- p) print(aP)
else {
perm(n + 1, p, pi, dir)
for (i <- 0 until n) { // swap
printf(" (%d %d)\n", pi(n), pi(n) + dir(n))
val z = p(pi(n) + dir(n))
p(pi(n)) = z
p(pi(n) + dir(n)) = n
pi(z) = pi(n)
pi(n) = pi(n) + dir(n)
perm(n + 1, p, pi, dir)
}
dir(n) = -dir(n)
}
}
for (i <- 0 until n) {
dir(i) = -1
p(i) = i
pi(i) = i
}
perm(0, p, pi, dir)
print(" (0 1)\n")
}
perm(4)
}</lang>
{{Out}}See it in running in your browser by [https://scastie.scala-lang.org/DdM4xnUnQ2aNGP481zwcrw Scastie (JVM)].
=={{header|Sidef}}==
{{trans|Perl}}
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