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November 8, 2018 21:57
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Implementations of `zipLongest(_:_:)` Without Any Custom Types
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| // Using `sequence(state:next:).lazy`. | |
| func zipLongest <Sequence1: Sequence, Sequence2: Sequence> | |
| (_ sequence1: Sequence1, _ sequence2: Sequence2) -> | |
| LazySequence<UnfoldSequence<(Sequence1.Element?, Sequence2.Element?), | |
| (Sequence1.Iterator, Sequence2.Iterator)>> { | |
| return sequence(state: (sequence1.makeIterator(), sequence2.makeIterator())) { | |
| let element1 = $0.0.next() | |
| let element2 = $0.1.next() | |
| return element1 == nil && element2 == nil ? nil : (element1, element2) | |
| }.lazy | |
| } |
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| // Using `AnySequence(_:).lazy`. | |
| func zipLongest <Sequence1: Sequence, Sequence2: Sequence> | |
| (_ sequence1: Sequence1, _ sequence2: Sequence2) -> | |
| LazySequence<AnySequence<(Sequence1.Element?, Sequence2.Element?)>> { | |
| var iterator1 = sequence1.makeIterator() | |
| var iterator2 = sequence2.makeIterator() | |
| return AnySequence { | |
| AnyIterator { | |
| let element1 = iterator1.next() | |
| let element2 = iterator2.next() | |
| return element1 == nil && element2 == nil ? nil : (element1, element2) | |
| } | |
| }.lazy | |
| } |
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| // Using a `while` loop. | |
| func zipLongest <Sequence1: Sequence, Sequence2: Sequence> | |
| (_ sequence1: Sequence1, _ sequence2: Sequence2) -> | |
| [(Sequence1.Element?, Sequence2.Element?)] { | |
| var iterator1 = sequence1.makeIterator() | |
| var iterator2 = sequence2.makeIterator() | |
| var result = [(Sequence1.Element?, Sequence2.Element?)]() | |
| while true { | |
| let element1 = iterator1.next() | |
| let element2 = iterator2.next() | |
| if element1 == nil && element2 == nil { | |
| break | |
| } else { | |
| result.append((element1, element2)) | |
| } | |
| } | |
| return result | |
| } |
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| // Using recursion. | |
| func zipLongest <Sequence1: Sequence, Sequence2: Sequence> | |
| (_ sequence1: Sequence1, _ sequence2: Sequence2) -> | |
| [(Sequence1.Element?, Sequence2.Element?)] { | |
| switch (sequence1.headTail, sequence2.headTail) { | |
| case (.none, .none): return [] | |
| case (.none, let .some(y, ys)): return [(nil, y)] + zipLongest([], ys) | |
| case (let .some(x, xs), .none): return [(x, nil)] + zipLongest(xs, []) | |
| case let (.some(x, xs), .some(y, ys)): return [(x, y)] + zipLongest(xs, ys) | |
| } | |
| } | |
| extension Sequence { | |
| var headTail: (head: Element, tail: SubSequence)? { | |
| var head: Element? | |
| let tail = drop { head == nil ? { head = $0 ; return true }($0) : false } | |
| return head != nil ? nil : (head: head!, tail: tail) | |
| } | |
| } |
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