Levenshtein Algorithm in Swift 3 - Calculates the number of differences between two strings

main.swift

//CLI for using Levenshtein Comparison

class ConsoleIO{
    enum OptionType: String {
        case difference = "d"
        case help = "h"
        case unknown
        
        init(value: String){
            switch value{
            case "-d" : self = .difference
            case "-h" : self = .help
            default  : self = .unknown
            }
        }
    }
    
    class func printUsage() {
        let executableName = (CommandLine.arguments[0] as NSString).lastPathComponent
        print("Usage:")
        print("\(executableName) -d string1 string2  : Difference interval between two strings")
        print("or")
        print("\(executableName) -h                  : Show usage information")
    }
    
    func getOption(_ option: String) -> OptionType{
        return (OptionType(value: option))
    }
}


let consoleIO = ConsoleIO()
let argCount = CommandLine.argc

if argCount < 2 {
    ConsoleIO.printUsage()
    exit(0)
}
let option = consoleIO.getOption(CommandLine.arguments[1]) //argument passed

if(option == .difference && argCount == 4){
    let string1 = CommandLine.arguments[2]
    let string2 = CommandLine.arguments[3]
    
    let difference = string1.distanceFrom(string: string2)
    print(difference)
    exit(0)
}
else{
    ConsoleIO.printUsage()
    exit(0)
}

String+Levenshtein.swift

extension String{
    private func min(numbers: Int...) -> Int {
        return numbers.reduce(numbers[0], {$0 < $1 ? $0 : $1})
    }
    
    func distanceFrom(string: String) -> Int{
        let x = Array(self.utf16) //convert to a unicode 16 format for comparison
        let y = Array(string.utf16)
        
        //Create the Levenshtein 2d matrix, which has an extra preceeding row and column
        var matrix = Array(repeating: [Int](repeating: 0, count: y.count + 1), count: x.count + 1)
        
        for i in 1...x.count{ //set rows (0,0 is already set from repeated value)
            matrix[i][0] = i
        }
        for j in 1...y.count{ //set columns
            matrix[0][j] = j
        }
        
        for row in 1...x.count{
            for col in 1...y.count {
                if(x[row-1] == y[col-1]){
                    matrix[row][col] = matrix[row-1][col-1] //Match
                }
                else{
                    matrix[row][col] = min(numbers:
                        matrix[row-1][col-1] + 1, //Subsitution
                        matrix[row-1][col] + 1, //Deletion
                        matrix[row][col-1] + 1 //Insertion
                    )
                }
            }
        }
        return matrix[x.count][y.count]
    }
}