Numeric Progressions

main.swift

/// - Note: this requires Swift 3.0 (Mac OS X or iOS, Linux currently crashes in locale fetching)
import Foundation

func permuteLetterCountCycles(_ start: Int, _ formatter: NumberFormatter) -> [String] {
    var foundNumbers = Set<Int>()
    var result = Array<String>()
    var number = start
    formatter.numberStyle = .spellOut
    while true {
        // convert the number into the string representation (and presume all locales have a string representation)
        let str = formatter.string(from: NSNumber(value: number))!
         // count the grapheme clusters for the number word
        let count = str.characters.count
        // add the progression of strings to the resultant array
        result.append(str)
        // if there is a cycle then terminate the permutation
        if foundNumbers.contains(count) {
            break
        }
        // record the number so that cycle detection can terminate before an infinite loop
        foundNumbers.insert(count)
        // the next input to the conversion is the resultant length
        number = count
    }
    return result
}

let formatter = NumberFormatter()

var longestGlobalChain: [String]?
var longestGlobalLocale: Locale?

for locale in Locale.availableIdentifiers.map({ Locale(identifier: $0) }) {
    formatter.locale = locale
    var longestChain: [String]?
    // iterating past 1000 can potentially be slow
    for idx in 0..<1000 {
        let chain = permuteLetterCountCycles(idx, formatter)
        // record the longest chain of number to string representations for this locale
        if let prevChain = longestChain {
            if prevChain.count < chain.count {
                longestChain = chain
            }
        } else {
            longestChain = chain
        }
    }
    
    // record the longest chain of number to string representations for all locales
    if let prevChain = longestGlobalChain {
        if prevChain.count < longestChain!.count {
            longestGlobalChain = longestChain
            longestGlobalLocale = locale
        }
    } else {
        longestGlobalChain = longestChain
        longestGlobalLocale = locale
    }
    
    print("\(Locale.current.localizedString(forIdentifier: locale.identifier)!) (\(longestChain!.count)) \(longestChain!)")
}

print("\(Locale.current.localizedString(forIdentifier: longestGlobalLocale!.identifier)!) \(longestGlobalChain!.count) \(longestGlobalChain!)")