progs/pow.scala
author Christian Urban <urbanc@in.tum.de>
Tue, 25 Sep 2018 20:50:42 +0100
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def concat(A: Set[String], B: Set[String]) : Set[String] =
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  for (x <-A ; y <- B) yield x ++ y
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def pow(A: Set[String], n: Int) : Set[String] = n match {
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  case 0 => Set("")
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  case n => concat(A, pow(A, n- 1))
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}
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val A = Set("a", "b", "c", "d")
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pow(A, 4).size                            // -> 256
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val B = Set("a", "b", "c", "")
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pow(B, 4).size                            // -> 121
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val B2 = Set("a", "b", "c", "")
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pow(B2, 3).size                           // -> 40
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val C = Set("a", "b", "")
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pow(C, 2)
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pow(C, 2).size                            // -> 7
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pow(C, 3)
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pow(C, 3).size                            // -> 15
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val A = Set("a", "b", "c", "d")
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pow(A, 4).size   
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val A = Set("a", "b", "c")
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pow(A, 5).size   
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val A = Set("a", "b", "")
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pow(A, 5).size