37 lines
752 B
Scala
37 lines
752 B
Scala
import scala.annotation.tailrec
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// 3.1
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def product(f: Int => Double)(a: Int)(b: Int): Double = {
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@tailrec
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def iter(i: Int, prod: Double): Double =
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if (i > b) prod
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else iter(i + 1, prod * f(i))
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iter(a, 1)
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}
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product(x => x)(3)(5)
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// 3.2
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def factorial(n: Int): Double = product(i => if (i == 0) {1} else {i})(0)(n)
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factorial(5)
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// 3.3
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def mapReduce(red: (Double, Double) => Double)(v0: Double)(f: Int => Double)(a: Int)(b: Int) = {
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@tailrec
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def iter(i: Int, acc: Double): Double =
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if (i > b) acc
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else iter(i + 1, red(acc, f(i)))
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iter(a, v0)
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}
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val sum = mapReduce((a, b) => a + b)(0) _
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val prod = mapReduce((a, b) => a * b)(1) _
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sum(i => i)(1)(5)
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prod(i => i)(1)(5)
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mapReduce((a, b) => a + b)(0)(i => 2 * i + 1)(1)(5) |