James Strachan
60 lines
2.4 KiB
Kotlin
60 lines
2.4 KiB
Kotlin
package iterators
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import kotlin.test.assertEquals
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import org.junit.Test
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class IteratorsTest {
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private fun fibonacci(): java.util.Iterator<Int> {
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// fibonacci terms
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var index = 0; var a = 0; var b = 1
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return iterate<Int> { when (index++) { 0 -> a; 1 -> b; else -> { val result = a + b; a = b; b = result; result } } }
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}
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Test fun filterAndTakeWhileExtractTheElementsWithinRange() {
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assertEquals(arrayList(144, 233, 377, 610, 987), fibonacci().filter { it > 100 }.takeWhile { it < 1000 }.toList())
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}
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Test fun foldReducesTheFirstNElements() {
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val sum = { (a: Int, b: Int) -> a + b }
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assertEquals(arrayList(13, 21, 34, 55, 89).fold(0, sum), fibonacci().filter { it > 10 }.take(5).fold(0, sum))
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}
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Test fun takeExtractsTheFirstNElements() {
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assertEquals(arrayList(0, 1, 1, 2, 3, 5, 8, 13, 21, 34), fibonacci().take(10).toList())
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}
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Test fun mapAndTakeWhileExtractTheTransformedElements() {
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assertEquals(arrayList(0, 3, 3, 6, 9, 15), fibonacci().map { it * 3 }.takeWhile { (i: Int) -> i < 20 }.toList())
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}
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Test fun flatMapAndTakeExtractTheTransformedElements() {
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fun intToBinaryDigits() = { (i: Int) ->
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val binary = Integer.toBinaryString(i).sure()
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var index = 0
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iterate<Char> { if (index < binary.length()) binary.get(index++) else null }
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}
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val expected = arrayList(
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'0', // fibonacci(0) = 0
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'1', // fibonacci(1) = 1
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'1', // fibonacci(2) = 1
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'1', '0', // fibonacci(3) = 2
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'1', '1', // fibonacci(4) = 3
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'1', '0', '1' // fibonacci(5) = 5
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)
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assertEquals(expected, fibonacci().flatMap<Int, Char>(intToBinaryDigits()).take(10).toList())
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}
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Test fun joinConcatenatesTheFirstNElementsAboveAThreshold() {
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assertEquals("13, 21, 34, 55, 89, ...", fibonacci().filter { it > 10 }.join(separator = ", ", limit = 5))
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}
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Test fun toStringJoinsNoMoreThanTheFirstTenElements() {
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assertEquals("0, 1, 1, 2, 3, 5, 8, 13, 21, 34, ...", fibonacci().join(limit = 10))
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assertEquals("13, 21, 34, 55, 89, 144, 233, 377, 610, 987, ...", fibonacci().filter { it > 10 }.join(limit = 10))
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assertEquals("144, 233, 377, 610, 987", fibonacci().filter { it > 100 }.takeWhile { it < 1000 }.join())
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}
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}
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