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  1. object Main {
  2.  
  3. type Matrix = IndexedSeq[IndexedSeq[IndexedSeq[Int]]]
  4.  
  5.   def initial(folds: Int): Matrix = {
  6.     val sideLen = math.pow(2, folds / 2).toInt
  7.     (1 to sideLen * sideLen) map (Vector(_)) grouped sideLen toIndexedSeq
  8.   }
  9.  
  10.   def leftFold (m: Matrix): Matrix = m map { r => 
  11.     val (a, b) = r splitAt (r.size / 2) 
  12.     (a.reverse, b).zipped map (_.reverse ++ _)
  13.   }
  14.  
  15.   def rightFold(m: Matrix): Matrix = m map { r => 
  16.     val (a, b) = r splitAt (r.size / 2) 
  17.     (b.reverse, a).zipped map (_.reverse ++ _)
  18.   }
  19.  
  20.   def topFold   (m: Matrix): Matrix = leftFold(m.transpose).transpose
  21.   def bottomFold(m: Matrix): Matrix = rightFold(m.transpose).transpose
  22.  
  23.   def fold(input: String): Seq[Int] = {
  24.     def go(in: String, m: Matrix): Seq[Int] = in match {
  25.       case "" => m(0)(0)
  26.       case s  => go(s.tail, s.head match {
  27.         case 'L' => leftFold(m)
  28.         case 'R' => rightFold(m)
  29.         case 'T' => topFold(m)
  30.         case 'B' => bottomFold(m)
  31.       })
  32.     }
  33.     go(input, initial(input.length))
  34.   }
  35.  
  36. def unfold(input: Seq[Int]): String = { 
  37.     val m0: Matrix = Vector(Vector(Vector(input: _*)))
  38.     val sideLen = math.sqrt(input.length).toInt 
  39.  
  40.     def go(m: Matrix, out: String): String = {
  41.       val tl = m.head.head
  42.       if (m.length == sideLen && m.head.length == sideLen) out.reverse
  43.       else if (tl.head == tl.last - 1)       go(leftUnfold(m),   out + 'L')
  44.       else if (tl.head == tl.last + 1)       go(rightUnfold(m),  out + 'R')
  45.       else if (tl.head == tl.last - sideLen) go(topUnfold(m),    out + 'T')
  46.       else if (tl.head == tl.last + sideLen) go(bottomUnfold(m), out + 'B')
  47.       else sys.error("no fold found " + m) 
  48.     }
  49.     go(m0, "")
  50.   }    
  51.  
  52.   def leftUnfold (m: Matrix): Matrix = m map { r =>
  53.     val (a, b) = r.map(e => e.splitAt(e.size / 2)).unzip
  54.     a.map(_.reverse).reverse ++ b
  55.   }
  56.  
  57.   def rightUnfold(m: Matrix): Matrix = m map { r =>
  58.     val (a, b) = r.map(e => e.splitAt(e.size / 2)).unzip
  59.     b ++ a.map(_.reverse).reverse
  60.   }
  61.  
  62.   def topUnfold   (m: Matrix): Matrix = leftUnfold (m.transpose).transpose
  63.   def bottomUnfold(m: Matrix): Matrix = rightUnfold(m.transpose).transpose
  64.  
  65.   def main(args: Array[String]) {
  66.     println(fold("RBLT"))
  67.     println(unfold(fold("RBLT")))
  68.   }
  69. }
Runtime error #stdin #stdout 0.33s 247552KB
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Standard input is empty
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Vector(2, 3, 15, 14, 13, 16, 4, 1, 5, 8, 12, 9, 10, 11, 7, 6)
https://ideone.com/YYpkF
language:
Scala (scala 2.12.8)
created:
13 years ago
visibility:
public

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