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Signed-off-by: Andreas Roehler <[email protected]>
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/** | ||
Exercise 2.2.6.2 | ||
Implement the flatten method for sequences by using foldLeft. | ||
The required type signature and a sample test are: | ||
def flatten[A](xxs: Seq[Seq[A]]): Seq[A] = ??? | ||
scala> flatten(Seq(Seq(1, 2, 3), Seq(), Seq(4))) | ||
res0: Seq[Int] = List(1, 2, 3, 4) | ||
scala> flatten(Seq(Seq("a","b"), Seq(), (Seq("c","<nothing>")))) | ||
val res1: Seq[String] = List(a, b, c, <nothing>) | ||
*/ | ||
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object Flatten { | ||
def flatten[A](xxs: Seq[Seq[A]]): Seq[A] = { | ||
var init: Seq[A] = Seq() | ||
xxs.foldLeft(init){ (x, y) => y.foreach( k => (init = init :+ k)); init} | ||
} | ||
def main(args: Array[String]): Unit = { | ||
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val result = flatten(Seq(Seq(1, 2, 3), Seq(), Seq(4))) | ||
val expected: Seq[Int] = List(1, 2, 3, 4) | ||
println("result: %s".format(result)) | ||
println("expected: %s".format(expected)) | ||
assert(result == expected) | ||
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val a = flatten(Seq(Seq("a","b"), Seq(), (Seq("c","<nothing>")))) | ||
val b: Seq[String] = List("a", "b", "c", "<nothing>") | ||
assert(a == b) | ||
} | ||
Flatten.main(Array()) | ||
} | ||
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Flatten.main(Array()) | ||
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// scala> :load solution2.2.6.2_main.scala | ||
// :load solution2.2.6.2_main.scala | ||
// result: List(1, 2, 3, 4) | ||
// expected: List(1, 2, 3, 4) | ||
// // defined object Flatten |