Numbers.swift

import Foundation

extension Int {
	var rank: Int {
		return self > 0 ? (Int(log10(Double(self)) + 1)) : 1
	}

	func expToRank(rank: Int) -> Int {
		return self * Int(pow(10, Double(rank - self.rank)))
	}
}

let array = [50, 2, 1, 9]
let maxRank = array.map { $0.rank }.reduce(0) { max($0, $1) }
let finalArray = array.sorted {	return $0.expToRank(maxRank) >= $1.expToRank(maxRank) }
var finalNumber = 0

for (index, input) in enumerate(finalArray) {
	finalNumber += input

	if index + 1 < finalArray.count {
		finalNumber *= Int(pow(10, Double(finalArray[index + 1].rank)))
	}
}

println(finalNumber)