Solution for the Trello iOS coding challenge

TrelloHash.swift

//
//  TrelloHash.swift
//  TrelloHash
//
//  Created by Ian Guedes Maia on 09/02/16.
//  Copyright © 2016 Ian Guedes Maia. All rights reserved.
//

import Foundation

//MARK: - trello hash

func hash(s: String) -> Int64 {
    var h:Int64 = 7
    let letters = "acdegilmnoprstuw"
    for(var i = 0; i < s.characters.count; i++) {
        h = (h * 37 + letters.indexOf(s[i]))
    }
    return h
}

//MARK: - reverse hash

func reverseHashRecursive(let code: Int) -> String {
    let letters = "acdegilmnoprstuw"
    
    let remaining = (code - (code % 37)) / 37
    
    if (code > letters.characters.count) {
        return reverseHashRecursive(remaining) + letters[code % 37]
    } else {
        return "";
    }
}

func reverseHash(var code: Int) -> String {
    let letters = "acdegilmnoprstuw"
    
    var hash: String = ""
    while code > letters.characters.count  {
        hash.append(letters[code % 37].characters.first!)
        code = (code - (code % 37)) / 37
    }
    
    //ha!
    return String(hash.characters.reverse())
}

//MARK: - util

extension String {
    subscript (i: Int) -> String {
        return String(self[self.startIndex.advancedBy(i)])
    }
    
    func indexOf(target: String) -> Int {
        let range = self.rangeOfString(target)
        if let range = range {
            return self.startIndex.distanceTo(range.startIndex)
        } else {
            return -1
        }
    }
}

//MARK: - main

print(reverseHashRecursive(25377615533200))
print(reverseHash(25377615533200))

print(hash(reverseHash(25377615533200)) == 25377615533200)
print(hash(reverseHashRecursive(25377615533200)) == 25377615533200)