26 lines
774 B
Text
26 lines
774 B
Text
// purely functional & lazy version, leveraging recursion and Sequences (a.k.a. streams)
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fun <T> Set<T>.subsets(): Sequence<Set<T>> =
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when (size) {
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0 -> sequenceOf(emptySet())
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else -> {
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val head = first()
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val tail = this - head
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tail.subsets() + tail.subsets().map { setOf(head) + it }
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}
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}
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// if recursion is an issue, you may change it this way:
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fun <T> Set<T>.subsets(): Sequence<Set<T>> = sequence {
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when (size) {
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0 -> yield(emptySet<T>())
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else -> {
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val head = first()
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val tail = this@subsets - head
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yieldAll(tail.subsets())
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for (subset in tail.subsets()) {
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yield(setOf(head) + subset)
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}
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}
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}
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}
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