My dirty 2:30 AM solution for the Omni Group’s Swift Bike Shedding Club week two question: http://rubyquiz.com/quiz2.html (via Brent)

SecretSanta.swift

/*

sort families by their size. (let's name them A, B, C, D, and E.)
(if the biggest family is over half of the enitre group there's no valid solution.)
while A.count > B.count
	pair up santas from A (the biggest family) and E (the smallest)
	(e.g., Dan A is Brent E's santa and vice versa)

while there are still unmatched people
	make loops of people
	(e.g., Alex A is Brian B's santa. Brian is Clair C's santa, ..., and Eric E is Alex A's santa)

After each step of new santas make sure the smallest family isn't empty.
If it is empty just throw it out and treat the next one (D) as the smallest.

*/

import Foundation

struct Person: Hashable, CustomStringConvertible {
	var firstName: String
	var lastName: String

	init(_ name: String) {
		let nameParts = name.componentsSeparatedByString(" ")
		self.firstName = nameParts[0]
		self.lastName = nameParts[1]
	}

	var description: String {
		return "\(firstName) \(lastName)"
	}

	var hashValue: Int {
		return description.hashValue
	}
}

func ==(lhs: Person, rhs: Person) -> Bool {

    return lhs.hashValue == rhs.hashValue
}


func tally<T, S: Hashable>(array: [T], key: T -> S) -> [S: [T]] {
	var res: [S: [T]] = [:]
	for element in array {
		let k = key(element)
		res[k] = (res[k] ?? []) + [element]
	}
	return res
}


func findSantas(people: [Person]) -> [Person: Person]? {
	// Tally by last name, sort by family size.
	var families = tally(people, key: { person in person.lastName }).values.sort({ $0.count > $1.count })
	// Verify that the biggest family isn't too big.
	guard !families.isEmpty && families.first!.count <= people.count/2 else { return nil }
	
	var santas: [Person: Person] = [:]

	while families[0].count > families[1].count {
		let p1 = families[0].removeLast()
		let p2 = families[families.count-1].removeLast()
		santas[p1] = p2
		santas[p2] = p1

		if families.last?.isEmpty ?? false {
			families.removeLast()
		}
	}

	while !families.isEmpty {
		var previousGuy = families.last!.last!
		for i in 0..<families.count {
			let newGuy = families[i].removeLast()
			santas[previousGuy] = newGuy
			previousGuy = newGuy
		}
		while families.last?.isEmpty ?? false {
			families.removeLast()
		}
	}

	return santas
}


let people1 = [Person("Luke Skywalker"), Person("Leia Skywalker"), Person("Toula Portokalos"), Person("Gus Portokalos"), Person("Bruce Wayne"), Person("Virgil Brigman"), Person("Lindsey Brigman"), Person("Franz Kafka"), Person("Courtney Kafka"), Person("Skip Kafka"), Person("Aloysius Kafka")]
let people2 = [Person("Luke Skywalker"), Person("Leia Skywalker"), Person("Toula Portokalos")]

print("Solution exists: \(findSantas(people1))") // valid
print("Solution doesn't exist: \(findSantas(people2))") // returns nil