/
SetExtensions.swift
84 lines (69 loc) · 1.84 KB
/
SetExtensions.swift
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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
import Foundation
public extension SetIterator {
mutating func take(_ n: Int) -> [Element]? {
precondition(n >= 0)
if n == 0 {
return []
}
var count: Int = 0
var out: [Element] = []
while count < n {
count += 1
guard let val = self.next() else {
if out.isEmpty {
return nil
}
return out
}
out.append(val)
}
return out
}
}
public extension Set {
func withSubsetsOfSize(_ n: Int, f: (Set<Iterator.Element>) -> Void) {
precondition(n > 0)
if self.isEmpty {
return
}
if n > self.count {
f(self)
return
}
if n == 1 {
self.forEach { f(Set([$0])) }
return
}
var generator = self.makeIterator()
while let next = generator.take(n) {
if !next.isEmpty {
f(Set(next))
}
}
}
func subsetsOfSize(_ n: Int) -> [Set<Iterator.Element>] {
precondition(n > 0)
if self.isEmpty {
return []
}
if n > self.count {
return [self]
}
if n == 1 {
// Special case.
return self.map({ Set([$0]) })
}
var generator = self.makeIterator()
var out: [Set<Iterator.Element>] = []
out.reserveCapacity(self.count / n)
while let next = generator.take(n) {
if !next.isEmpty {
out.append(Set(next))
}
}
return out
}
}