如何在Swift中实现ROT13函数？

Question

我想创建一个函数，它接收一个字符串并返回一个字符串，并用字母后面的13个字母替换一个字母（ROT13）。我发现了很多例子，不幸的是，由于各种错误，我无法让它工作。例如，这一个：

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

其实你的映射Character S的初步做法是好的：

var key = [Character: Character]() 

但两个数组必须是Characters数组：

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

（备注：您（几乎）不想致电xxxLiteral:初始化程序 明确。这样做是（几乎）总是躲在实际问题）

现在你的代码来填充字典的工作：

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

和转化的字符串是可以做到

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

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

Answer 2

这里的另一个方法，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) 

Answer 3

这是@AMomch的替代版本它采用了switch少数学和ilov的rot13消除幻数：

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!" 

---

泛化rotN

我已经让他们采取采取rot13功能上面，并推广他们rotN一组ClosedInterval<UnicodeScalar>。这允许您以非常直接的方式实施rot13,rot47,rot5以及rot13和rot5的组合。

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

    for interval in intervals { 
     let half = (interval.end.value - interval.start.value + 1)/2 
     let halfway = UnicodeScalar(interval.start.value + half) 

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

    return Character(UnicodeScalar(result)) 
} 

func rotN(input: String, intervals:[ClosedInterval<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" 

---

这是基于的rotN版本在原有@AMomchilov'srot13：

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

    for interval in intervals { 
     let start = interval.start.value 
     let length = interval.end.value - start + 1 

     if interval ~= unicodeScalar { 
      result = (result + length/2 - start) % length + start 
     } 
    } 

    return UnicodeScalar(result) 
} 


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