Ordered words in Swift

ordered-words.swift

/**
http://rosettacode.org/wiki/Ordered_words
Define an ordered word as a word in which the letters of the word appear in alphabetic order. Examples include 'abbey' and 'dirt'.
The task is to find and display all the ordered words in this dictionary that 
have the longest word length. 
(Examples that access the dictionary file locally assume that you have downloaded this file yourself.) 

The display needs to be shown on this page.
*/

import Foundation
 
guard
    let url =  NSURL(string: "http://www.puzzlers.org/pub/wordlists/unixdict.txt"),
    let input = try? NSString(contentsOfURL: url,encoding: NSUTF8StringEncoding) as String
    else { exit(EXIT_FAILURE) }
 
let words = input.componentsSeparatedByCharactersInSet(NSCharacterSet.newlineCharacterSet())
let group: ([Int: [String]], String) -> [Int: [String]] = {
    var d = $0; let g = d[$1.characters.count] ?? []
    d[$1.characters.count] = g + [$1]
    return d
}
let ordered: ([String], String) -> [String] = {
    guard String($1.characters.sort()) == $1 else { return $0 }
    return $0 + [$1]
}
 
let groups = words
    .reduce([String](), combine: ordered)
    .reduce([Int: [String]](), combine: group)
 
guard
    let maxLength = groups.keys.maxElement(),
    let maxLengthGroup = groups[maxLength]
    else { exit(EXIT_FAILURE) }
 
maxLengthGroup.forEach { print($0) }

/** 
outputs:
========
abbott
accent
accept
access
accost
almost
bellow
billow
biopsy
chilly
choosy
choppy
effort
floppy
glossy
knotty
*/