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// Combos benchmark
//
// Description: Generates every combination of every element in two sequences
// Source: https://gist.github.com/airspeedswift/34251f2ddb1b038c5d88
import TestsUtils
public let benchmarks =
BenchmarkInfo(
name: "Combos",
runFunction: run_Combos,
tags: [.validation, .abstraction]
)
@inline(never)
public func run_Combos(_ n: Int) {
let firstRef = [Character("A"), Character("0")]
let lastRef = [Character("J"), Character("9")]
var combos = [[Character]]()
for _ in 1...10*n {
combos = combinations("ABCDEFGHIJ", "0123456789").map {
return [$0] + [$1]
}
if combos.first! != firstRef || combos.last! != lastRef {
break
}
}
check(combos.first! == firstRef && combos.last! == lastRef)
}
func combinations
<First: Sequence, Second: Collection>
(_ first: First, _ second: Second)
-> AnyIterator<(First.Element, Second.Element)> {
var first_gen = first.makeIterator()
var second_gen = second.makeIterator()
var current_first = first_gen.next()
return AnyIterator {
// check if there's more of first to consume
if let this_first = current_first {
// if so, is there more of this go-around
// of second to consume?
if let this_second = second_gen.next() {
return (this_first, this_second)
}
// if second used up, reset it
else {
// go back to the beginning of second
second_gen = second.makeIterator()
// and take the first element of it
let next_second = second_gen.next()
// was there a first element?
if let this_second = next_second {
// move on to the next element of first
current_first = first_gen.next()
// is there such an element?
if let this_first = current_first {
return (this_first, this_second)
}
// if not, we've reached the end of
// the first sequence
else {
// so we've finished
return nil
}
}
// if not, second is empty
else {
// so we need to guard against
// infinite looping in that case
return nil
}
}
}
// if not, we've reached the end of
// the first sequence
else {
// so we've finished
return nil
}
}
}
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