Xpre 11•Swift 5.1
extension Collection { func choose(_ n: Int) -> ArraySlice<Element> { shuffled().prefix(n) }}游乐场测试
var alphabet = ["A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z"]let shuffledAlphabet = alphabet.shuffled() // "O", "X", "L", "D", "N", "K", "R", "E", "S", "Z", "I", "T", "H", "C", "U", "B", "W", "M", "Q", "Y", "V", "A", "G", "P", "F", "J"]let letter = alphabet.randomElement() // "D"var numbers = Array(0...9)let shuffledNumbers = numbers.shuffled()shuffledNumbers // [8, 9, 3, 6, 0, 1, 4, 2, 5, 7]numbers // [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]numbers.shuffle() // mutate it [6, 0, 2, 3, 9, 1, 5, 7, 4, 8]numbers // [6, 0, 2, 3, 9, 1, 5, 7, 4, 8]let pick3numbers = numbers.choose(3) // [8, 9, 2]
extension RangeReplaceableCollection { /// Returns a new Collection shuffled var shuffled: Self { .init(shuffled()) } /// Shuffles this Collection in place @discardableResult mutating func shuffledInPlace() -> Self { self = shuffled return self } func choose(_ n: Int) -> SubSequence { shuffled.prefix(n) }}var alphabetString = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"let shuffledAlphabetString = alphabetString.shuffled // "DRGXNSJLFQHPUZTBKVMYAWEICO"let character = alphabetString.randomElement() // "K"alphabetString.shuffledInPlace() // mutate it "WYQVBLGZKPFUJTHOXERADMCINS"alphabetString // "WYQVBLGZKPFUJTHOXERADMCINS"let pick3Characters = alphabetString.choose(3) // "VYA"
