如何在Swift中实现ROT13函数？

Question

我想要创建一个函数，它接收一个字符串并返回一个字符串，并在字母(ROT13)后面用13个字母替换一个字母。我发现了很多例子，不幸的是，由于各种错误，我没能让它正常工作。例如，这个：

var key = [String:String]() // EDITED
let uppercase = Array(arrayLiteral: "ABCDEFGHIJKLMNOPQRSTUVWXYZ")
let lowercase = Array(arrayLiteral: "abcdefghijklmnopqrstuvwxyz")
for i in 0 ..< 26 {
    key[uppercase[i]] = uppercase[(i + 13) % 26]
    key[lowercase[i]] = lowercase[(i + 13) % 26]
}

func rot13(s: String) -> String {
    return String(map(s, { key[$0] ?? $0 }))
}

Answer 1

实际上，您最初映射Characters的方法很好：

var key = [Character: Character]()

但是这两个数组必须是Characters的be数组

let uppercase = Array("ABCDEFGHIJKLMNOPQRSTUVWXYZ".characters)
let lowercase = Array("abcdefghijklmnopqrstuvwxyz".characters)

(注意:您(几乎)从来不想显式地调用xxxLiteral:初始化器。这样做(几乎)总是隐藏实际问题。

现在，填充字典的代码起作用了：

for i in 0 ..< 26 {
    key[uppercase[i]] = uppercase[(i + 13) % 26]
    key[lowercase[i]] = lowercase[(i + 13) % 26]
}

并且可以将字符串转换为

//                       map
// String --> Characters ---> Characters -> String

func rot13(s: String) -> String {
    return String(s.characters.map { key[$0] ?? $0 })
}

Answer 2

这是@AMomchilov的rot13的另一个版本，它使用了一个switch和更少的数学，并消除了神奇的数字：

func rot13(_ unicodeScalar: UnicodeScalar) -> Character {
    var result = unicodeScalar.value
    
    switch unicodeScalar {
    case "A"..."M", "a"..."m":
        result += 13
    case "N"..."Z", "n"..."z":
        result -= 13
    default:
        break
    }
    
    return Character(UnicodeScalar(result)!)
}

func rot13(_ input: String) -> String {
    return String(input.unicodeScalars.map(rot13))
}

print(rot13("Uryyb, jbeyq!")) // "Hello, world!"

对rotN的推广

我使用了上面的rot13函数，并通过让它们接受一个ClosedRange<UnicodeScalar>数组将它们推广到了rotN。这允许您以非常简单的方式实现rot13、rot47、rot5以及rot13和rot5的组合。

func rotN(_ unicodeScalar: UnicodeScalar, intervals:[ClosedRange<UnicodeScalar>]) -> Character {
    var result = unicodeScalar.value

    for interval in intervals {
        let half = (interval.upperBound.value - interval.lowerBound.value + 1) / 2
        let halfway = UnicodeScalar(interval.lowerBound.value + half)!

        switch unicodeScalar {
        case interval.lowerBound..<halfway:
            result += half
        case halfway...interval.upperBound:
            result -= half
        default:
            break
        }
    }

    return Character(UnicodeScalar(result)!)
}

func rotN(_ input: String, intervals:[ClosedRange<UnicodeScalar>]) -> String {
    return String(input.unicodeScalars.map {rotN($0, intervals: intervals)})
}

func rot13(_ input: String) -> String {
    return rotN(input, intervals:["A"..."Z", "a"..."z"])
}

func rot47(_ input: String) -> String {
    return rotN(input, intervals:["!"..."~"])
}

func rot5(_ input: String) -> String {
    return rotN(input, intervals:["0"..."9"])
}

func rot13and5(_ input: String) -> String {
    return rotN(input, intervals:["A"..."Z", "a"..."z", "0"..."9"])
}

print(rot13("Uryyb, jbeyq!"))        // "Hello, world!"
print(rot47("%96 BF:4< 3C@H? 7@I"))  // "The quick brown fox"
print(rot5("6 + 7 = 8"))             // "1 + 2 = 3"
print(rot13and5("Whyl 9, 6221"))     // "July 4, 1776"

下面是一个基于rotN的@AMomchilov's原始rot13的版本

func rotN(_ unicodeScalar: UnicodeScalar, intervals:[ClosedRange<UnicodeScalar>]) -> UnicodeScalar {
    var result = unicodeScalar.value
    
    for interval in intervals {
        let start = interval.lowerBound.value
        let length = interval.upperBound.value - start + 1
        
        if interval ~= unicodeScalar {
            result = (result + length/2 - start) % length + start
        }
    }
    
    return UnicodeScalar(result)!
}

func rotN(_ input: String, intervals:[ClosedRange<UnicodeScalar>]) -> String {
    return String(input.unicodeScalars.map {Character(rotN($0, intervals:intervals))})
}

Answer 3

下面是另一种方法，它不使用查找数组：

let input = "Hello World"

func rot13(unicodeScalar: UnicodeScalar) -> UnicodeScalar {
    var result = unicodeScalar.value

    if 65...90 ~= result { //Detect capital A ... Z
        result = (result + 13 - 65) % 26 + 65
    }
    else if 97 ... 122 ~= result { //Detect lowercase a ... z
        result = (result + 13 - 97) % 26 + 97
    }

    return UnicodeScalar(result)
}

func rot13(_ input: String) -> String {
    let resultUSs = input.unicodeScalars.map(rot13)

    var resultUSV = String.UnicodeScalarView()
    resultUSV.appendContentsOf(resultUSs) //for Swift 2.2
    //resultUSV.append(contentsOf: resultUSs) //for Swift 3.0
    return String(resultUSV)
}

let output = rot13(input)

print(output)