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Challenges Length of a Sumac Sequence

Scala, 83 bytes x=>x.init#::Stream.iterate(x)(x=>x++(x,x.tail).zipped.map(_-_))indexWhere(_.last<1) Try it online! Takes input as a list of two numbers. The fact that the length can...

posted 3y ago by user‭  ·  edited 3y ago by user‭

Answer
#2: Post edited by user avatar user‭ · 2021-04-24T23:28:56Z (over 3 years ago)
  • # [Scala], 83 bytes
  • <!-- language-all: lang-scala -->
  • x=>x.init#::Stream.iterate(x)(x=>x++(x,x.tail).zipped.map(_-_))indexWhere(_.last<1)
  • [Try it online!][TIO-knwd74v6]
  • [Scala]: http://www.scala-lang.org/
  • [TIO-knwd74v6]: https://tio.run/##bc0xa8MwEAXgPb/ioItEZGHZKUlMHMhYaKcOHUox1/hCLyiKsI8iGvLb3aRj0fSGj/feuEeP0/nzSHuBF@QAlIRCP8IuRrjMvtHDoYFnHuX9KcgHtFu4JbRTarfJcmB5aJpXGQhPloUGFFJJq7vO5yqZZAXZa/vDMVJvTxhVV3Rac@gpvX3RQKqzHkfZOD3FgYP4oA7qfqhcVRpYOq317L@UzsCiyshjeess1usM1aulgdxabaBw1SojRWWgzjf@zq/TLw "Scala – Try It Online"
  • Takes input as a list of two numbers. The fact that the length can be 0 makes this a bit longer. Explanation coming soon.
  • # [Scala], 83 bytes
  • <!-- language-all: lang-scala -->
  • x=>x.init#::Stream.iterate(x)(x=>x++(x,x.tail).zipped.map(_-_))indexWhere(_.last<1)
  • [Try it online!][TIO-knwd74v6]
  • [Scala]: http://www.scala-lang.org/
  • [TIO-knwd74v6]: https://tio.run/##bc0xa8MwEAXgPb/ioItEZGHZKUlMHMhYaKcOHUox1/hCLyiKsI8iGvLb3aRj0fSGj/feuEeP0/nzSHuBF@QAlIRCP8IuRrjMvtHDoYFnHuX9KcgHtFu4JbRTarfJcmB5aJpXGQhPloUGFFJJq7vO5yqZZAXZa/vDMVJvTxhVV3Rac@gpvX3RQKqzHkfZOD3FgYP4oA7qfqhcVRpYOq317L@UzsCiyshjeess1usM1aulgdxabaBw1SojRWWgzjf@zq/TLw "Scala – Try It Online"
  • Takes input as a list of two numbers. The fact that the length can be 0 makes this a bit longer.
  • ```
  • x => //List(t1, t2) a.k.a. the second partial sequence
  • x.init //List(t1) a.k.a. the first partial sequence
  • #:: //prepended to
  • Stream //an infinite stream of partial sequences
  • .iterate(x) //starting with the second partial sequence
  • (x => //to which this function is repeatedly applied:
  • x ++ //Concatenate the previous sequence to the next values
  • (x, x.tail).zipped //Zip the previous sequence and its tail
  • .map(_-_)) //And subtract each i-1th element from the ith element
  • indexWhere //Find the index of the sequence where
  • (_.last<1) //The last element is not positive
  • ```
#1: Initial revision by user avatar user‭ · 2021-04-24T23:20:07Z (over 3 years ago)
# [Scala], 83 bytes

<!-- language-all: lang-scala -->

    x=>x.init#::Stream.iterate(x)(x=>x++(x,x.tail).zipped.map(_-_))indexWhere(_.last<1)

[Try it online!][TIO-knwd74v6]

[Scala]: http://www.scala-lang.org/
[TIO-knwd74v6]: https://tio.run/##bc0xa8MwEAXgPb/ioItEZGHZKUlMHMhYaKcOHUox1/hCLyiKsI8iGvLb3aRj0fSGj/feuEeP0/nzSHuBF@QAlIRCP8IuRrjMvtHDoYFnHuX9KcgHtFu4JbRTarfJcmB5aJpXGQhPloUGFFJJq7vO5yqZZAXZa/vDMVJvTxhVV3Rac@gpvX3RQKqzHkfZOD3FgYP4oA7qfqhcVRpYOq317L@UzsCiyshjeess1usM1aulgdxabaBw1SojRWWgzjf@zq/TLw "Scala – Try It Online"

Takes input as a list of two numbers. The fact that the length can be 0 makes this a bit longer. Explanation coming soon.