如何在 Swift 中打乱数组? [英] How do I shuffle an array in Swift?
问题描述
如何在 Swift 中随机化或打乱数组中的元素?例如，如果我的数组由 52 张扑克牌组成，我想洗牌以洗牌.
How do I randomize or shuffle the elements within an array in Swift? For example, if my array consists of 52 playing cards, I want to shuffle the array in order to shuffle the deck.
推荐答案
这个答案详细说明了如何在 Swift 4.2+ 中使用快速且统一的算法 (Fisher-Yates) 进行 shuffle 以及如何在各个以前的版本中添加相同的功能斯威夫特的.每个 Swift 版本的命名和行为都与该版本的变异和非变异排序方法相匹配.
This answer details how to shuffle with a fast and uniform algorithm (Fisher-Yates) in Swift 4.2+ and how to add the same feature in the various previous versions of Swift. The naming and behavior for each Swift version matches the mutating and nonmutating sorting methods for that version.
shuffle 和 shuffled 是 Swift 4.2 的原生版本.示例用法:
shuffle and shuffled are native starting Swift 4.2. Example usage:
let x = [1, 2, 3].shuffled()
// x == [2, 3, 1]
let fiveStrings = stride(from: 0, through: 100, by: 5).map(String.init).shuffled()
// fiveStrings == ["20", "45", "70", "30", ...]
var numbers = [1, 2, 3, 4]
numbers.shuffle()
// numbers == [3, 2, 1, 4]
Swift 4.0 和 4.1
这些扩展添加了一个 shuffle() 方法到任何可变集合(数组和不安全的可变缓冲区)和一个 shuffled() 方法到任何序列:
Swift 4.0 and 4.1
These extensions add a shuffle() method to any mutable collection (arrays and unsafe mutable buffers) and a shuffled() method to any sequence:
extension MutableCollection {
/// Shuffles the contents of this collection.
mutating func shuffle() {
let c = count
guard c > 1 else { return }
for (firstUnshuffled, unshuffledCount) in zip(indices, stride(from: c, to: 1, by: -1)) {
// Change `Int` in the next line to `IndexDistance` in < Swift 4.1
let d: Int = numericCast(arc4random_uniform(numericCast(unshuffledCount)))
let i = index(firstUnshuffled, offsetBy: d)
swapAt(firstUnshuffled, i)
}
}
}
extension Sequence {
/// Returns an array with the contents of this sequence, shuffled.
func shuffled() -> [Element] {
var result = Array(self)
result.shuffle()
return result
}
}
与上面 Swift 4.2 示例中的用法相同.
Same usage as in Swift 4.2 examples above.
这些扩展添加了一个 shuffle() 方法到任何可变集合和一个 shuffled() 方法到任何序列:
These extensions add a shuffle() method to any mutable collection and a shuffled() method to any sequence:
extension MutableCollection where Indices.Iterator.Element == Index {
/// Shuffles the contents of this collection.
mutating func shuffle() {
let c = count
guard c > 1 else { return }
for (firstUnshuffled , unshuffledCount) in zip(indices, stride(from: c, to: 1, by: -1)) {
// Change `Int` in the next line to `IndexDistance` in < Swift 3.2
let d: Int = numericCast(arc4random_uniform(numericCast(unshuffledCount)))
guard d != 0 else { continue }
let i = index(firstUnshuffled, offsetBy: d)
self.swapAt(firstUnshuffled, i)
}
}
}
extension Sequence {
/// Returns an array with the contents of this sequence, shuffled.
func shuffled() -> [Iterator.Element] {
var result = Array(self)
result.shuffle()
return result
}
}
与上面 Swift 4.2 示例中的用法相同.
Same usage as in Swift 4.2 examples above.
(过时的语言:从 2018 年 7 月开始，您不能使用 Swift 2.x 在 iTunes Connect 上发布)
(obsolete language: you can't use Swift 2.x to publish on iTunes Connect starting July 2018)
extension MutableCollectionType where Index == Int {
/// Shuffle the elements of `self` in-place.
mutating func shuffleInPlace() {
// empty and single-element collections don't shuffle
if count < 2 { return }
for i in startIndex ..< endIndex - 1 {
let j = Int(arc4random_uniform(UInt32(count - i))) + i
guard i != j else { continue }
swap(&self[i], &self[j])
}
}
}
extension CollectionType {
/// Return a copy of `self` with its elements shuffled.
func shuffle() -> [Generator.Element] {
var list = Array(self)
list.shuffleInPlace()
return list
}
}
用法:
[1, 2, 3].shuffle()
// [2, 3, 1]
let fiveStrings = 0.stride(through: 100, by: 5).map(String.init).shuffle()
// ["20", "45", "70", "30", ...]
var numbers = [1, 2, 3, 4]
numbers.shuffleInPlace()
// [3, 2, 1, 4]
<小时>
斯威夫特 1.2
(过时的语言:从 2018 年 7 月开始，您不能使用 Swift 1.x 在 iTunes Connect 上发布)
Swift 1.2
(obsolete language: you can't use Swift 1.x to publish on iTunes Connect starting July 2018)
这个扩展可以让你将可变的 Array 实例混洗到位:
This extension will let you shuffle a mutable Array instance in place:
extension Array {
mutating func shuffle() {
if count < 2 { return }
for i in 0..<(count - 1) {
let j = Int(arc4random_uniform(UInt32(count - i))) + i
swap(&self[i], &self[j])
}
}
}
var numbers = [1, 2, 3, 4, 5, 6, 7, 8]
numbers.shuffle() // e.g., numbers == [6, 1, 8, 3, 2, 4, 7, 5]
shuffled 作为非变异数组方法
这个扩展可以让你检索一个 Array 实例的无序副本:
shuffled as a non-mutating array method
This extension will let you retrieve a shuffled copy of an Array instance:
extension Array {
func shuffled() -> [T] {
if count < 2 { return self }
var list = self
for i in 0..<(list.count - 1) {
let j = Int(arc4random_uniform(UInt32(list.count - i))) + i
swap(&list[i], &list[j])
}
return list
}
}
let numbers = [1, 2, 3, 4, 5, 6, 7, 8]
let mixedup = numbers.shuffled() // e.g., mixedup == [6, 1, 8, 3, 2, 4, 7, 5]
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