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Summarize and say sequence: Difference between revisions
→{{header|Ruby}}
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20 19281716151413427110
21 19182716152413228110</pre>
=={{header|Scala}}==
This example creates a ParVector, which is a collection type that inherently uses parallel processing, of all seeds within the range, maps each seed to a tuple containing the seed, the sequence, and the number of iterations, sorts the collection by decreasing sequence length, then shows the relevant information for the maximal sequences at the head of the collection.
<lang scala>import spire.math.SafeLong
import scala.annotation.tailrec
import scala.collection.parallel.immutable.ParVector
object SelfReferentialSequence {
def main(args: Array[String]): Unit = {
val nums = ParVector.range(1, 1000001).map(SafeLong(_))
val seqs = nums.map{ n => val seq = genSeq(n); (n, seq, seq.length) }.toVector.sortWith((a, b) => a._3 > b._3)
val maxes = seqs.takeWhile(t => t._3 == seqs.head._3)
println(s"Seeds: ${maxes.map(_._1).mkString(", ")}\nIterations: ${maxes.head._3}")
for(e <- maxes.distinctBy(a => nextTerm(a._1.toString))){
println(s"\nSeed: ${e._1}\n${e._2.mkString("\n")}")
}
}
def genSeq(seed: SafeLong): Vector[String] = {
@tailrec
def gTrec(seq: Vector[String], n: String): Vector[String] = {
if(seq.contains(n)) seq
else gTrec(seq :+ n, nextTerm(n))
}
gTrec(Vector[String](), seed.toString)
}
def nextTerm(num: String): String = {
@tailrec
def dTrec(digits: Vector[(Int, Int)], src: String): String = src.headOption match{
case Some(n) => dTrec(digits :+ ((n.asDigit, src.count(_ == n))), src.filter(_ != n))
case None => digits.sortWith((a, b) => a._1 > b._1).map(p => p._2.toString + p._1.toString).mkString
}
dTrec(Vector[(Int, Int)](), num)
}
}</lang>
{{out}}
<pre>Seeds: 9009, 9090, 9900
Iterations: 21
Seed: 9009
9009
2920
192210
19222110
19323110
1923123110
1923224110
191413323110
191433125110
19151423125110
19251413226110
1916151413325110
1916251423127110
191716151413326110
191726151423128110
19181716151413327110
19182716151423129110
29181716151413328110
19281716151423228110
19281716151413427110
19182716152413228110</pre>
=={{header|TXR}}==
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