Given a set of names, sort them in the following manner the next word should start with the last letter of the previous word. Swift implementation.

gistfile1.swift

import UIKit

var names = ["Luis", "Hector", "Selena", "Emmanuel", "Amish", "Rawle"]

var firsts = [String: String]()
var lasts = [String: String]()
var output = [String]()

for name in names {
    var key = (name as NSString).substringFromIndex(name.utf16Count-1)
    lasts[key] = name
    
    key = (name as NSString).substringToIndex(1).lowercaseString
    firsts[key] = name
}

for (key, val) in firsts {
    if lasts[key] == nil {
        output.append(val)
    }
}

while output.count < names.count {
    if output.count == 0 {
        output.append(names[0])
    }
    
    var last = output.last!
    var key = (last as NSString).substringFromIndex(last.utf16Count-1)
    output.append(firsts[key]!)
}

println(output)
// Returns ["Luis", "Selena", "Amish", "Hector", "Rawle", "Emmanuel"]