Problem: >If the numbers 1 to 5 are written out in words: one, two, three, four, five, then there are 3 + 3 + 5 + 4 + 4 = 19 letters used in total. >If all the numbers from 1 to 1000 (one thousand) inclusive were written out in words, how many letters would be used? >NOTE: Do not count spaces or hyphens. For example, 342 (three hundred and forty-two) contains 23 letters and 115 (one hundred and fifteen) contains 20 letters. The use of "and" when writing out numbers is in compliance with British usage. Solution: 21124 (Correct according to Project Euler). Since this hasn't been solved in Swift, I'd like a code review of this challenge which talks about the efficiency of the code, and how to optimise efficient, bad practices or violations of any concepts. Here is the code: import Foundation let unitNames:[String] = [ "", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen" ] let tensNames:[String] = [ "", "ten", "twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety", "hundred" ] func convertIntegerToWords(number:Int) -> String { var words:String = "" if number >= 0 && number <= 19 { words = words + unitNames[number] } else if number >= 20 && number <= 99 { var digits = number.array words = words + tensNames[digits[0]] words = words + unitNames[digits[1]] } else if number >= 100 && number <= 999 { var digits = number.array if number % 100 == 0 { words = words + unitNames[digits[0]] + "hundred"; } else { words = words + unitNames[digits[0]] + "hundredand"; var newNumber = number - digits[0] * 100; words = words + convertIntegerToWords(newNumber) } } else if number == 1000 { words = words + "onethousand" } return words } extension Int { var array: [Int] { return Array(description).map{String($0).toInt() ?? 0} } } func eulerSeventeen() -> Int { var length:Int = 0 for iterator in 1...1000 { length = length + count(convertIntegerToWords(iterator)) } return length } println(eulerSeventeen())