[Swift]遍历集合类型（数组、集合和字典）

★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★
➤微信公众号：山青咏芝（shanqingyongzhi）
➤博客园地址：山青咏芝（https://www.cnblogs.com/strengthen/ ）
➤GitHub地址：https://github.com/strengthen/LeetCode
➤原文地址：https://www.cnblogs.com/strengthen/p/9798475.html 
➤如果链接不是山青咏芝的博客园地址，则可能是爬取作者的文章。
➤原文已修改更新！强烈建议点击原文地址阅读！支持作者！支持原创！
★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★

Swift提供了三种主要的集合类型，称为数组，集合和字典，用于存储值集合。

数组是有序的值集合。

集是唯一值的无序集合。

字典是键值关联的无序集合。

Swift中无法再使用传统形式的for循环。

//传统for循环形式不适用于Swift
for（单次表达式;条件表达式;末尾循环体）{中间循环体；}

遍历数组：可以使用for- in循环遍历数组中的值。

let arrayStr:[String] = ["s","t","r","e","n","g","t","h","e","n","!"]

//方法1:根据元素顺序遍历
for item in arrayStr {
    print(item)
}

//方法2:根据部分元素顺序遍历
for item in arrayStr[1...5] {
    print(item)
}

//方法3：根据索引顺序遍历
for index in 0...(arrayStr.count - 1) {
    print(arrayStr[index])
}

//方法4:初始化数组并顺序遍历
for item in Array(1...10) {
    print(item)
}

//方法5：stride函数
//from，to，by 最后一个值是 >(或<) to的值
//from，through，by 最后一个值是 >=(或<=) through的值
for index in stride(from: 0, to: arrayStr.count,by: 1 )
{
    print(arrayStr[index])
}

如果不需要序列中的每个值，则可以使用下划线（_）代替变量名来忽略这些值。

let base = 3
let power = 10
var answer = 1
for _ in 1...power {
    answer *= base
}
print("\(base) to the power of \(power) is \(answer)")
// Prints "3 to the power of 10 is 59049"

遍历集合：可以使用for- in循环遍历集合中的值。

 let arrayStr:Set<String> = ["s","t","r","e","n","g"]
//输出的顺序是随机的
for item in arrayStr {
    print("\(item)")
}

Swift的Set类型没有定义的顺序。要以特定顺序迭代集合的值，请使用该sorted()方法，该方法将集合的元素作为使用<运算符排序的数组返回。

 let arrayStr:Set<String> = ["s","t","r","e","n","g"]
//按照字母排序顺序输出
for item in arrayStr.sorted() {
    print("\(item)")
}

遍历字典（可单独遍历键、值、或键值）

可以用字典遍历键值对for- in环。字典中的每个项都作为元组返回，您可以将元组的成员分解为临时常量或变量，作为迭代的一部分：(key, value),还可以通过访问字典的键keys和values属性来检索字典的键或值的可迭代集合：

var direc: [Int: String] =  [0:"s",1:"t",2:"r",3:"e",4:"n",5:"g"]

//按键值对遍历顺序遍历
for (num, char) in direc.sorted(by: <) {
    print("\(num): \(char)")
}

//按键遍历顺序遍历
for num in direc.keys.sorted(by: <) {
    print("\(num)")
}

//按值遍历顺序遍历
for char in direc.values {
    print("\(char)")
}

如果您需要使用带有Array实例的API的字典键或值，请使用keys或values属性初始化新数组：

let nums = [Int](direc.keys)
print(nums)
//次序随机 [4, 5, 2, 0, 1, 3]

let chars = [String](direc.values)
print(chars)
//次序随机 ["n", "g", "r", "s", "t", "e"]

Swift的Dictionary类型没有定义的顺序。要按特定顺序迭代字典的键或值，请sorted()在其keys或values属性上使用该方法。

倒序遍历 :reversed() 或 stride函数

Swift中标准库中方法

//可以用来快速的枚举数组中的内容，并用元组(index, value)接收
public func enumerated() -> EnumeratedSequence<Array<Element>>

//可以倒叙数组内容
public func reversed() -> ReversedRandomAccessCollection<Array<Element>>

当两者结合使用用到索引时需要注意

let arrayStr:[String] = ["s","t","r","e","n","g","t","h","e","n","!"]

//索引元素值绑定一起倒序遍历
for i in arrayStr.enumerated().reversed() {
  print("\(i) ", terminator: "")
}
/*
(offset: 10, element: "!") (offset: 9, element: "n") (offset: 8, element: "e") (offset: 7, element: "h") (offset: 6, element: "t") (offset: 5, element: "g") (offset: 4, element: "n") (offset: 3, element: "e") (offset: 2, element: "r") (offset: 1, element: "t") (offset: 0, element: "s") 
*/

//只元素值倒序遍历，原索引不变
for i in arrayStr.reversed().enumerated() {
  print("\(i) ", terminator: "")
}
/*
(offset: 0, element: "!") (offset: 1, element: "n") (offset: 2, element: "e") (offset: 3, element: "h") (offset: 4, element: "t") (offset: 5, element: "g") (offset: 6, element: "n") (offset: 7, element: "e") (offset: 8, element: "r") (offset: 9, element: "t") (offset: 10, element: "s") 
*/

倒序遍历数组

let arrayStr:[String] = ["s","t","r","e","n","g","t","h","e","n","!"]

//方法1:根据元素倒序遍历
for item in arrayStr.reversed() {
    print(item)
}

//方法2:根据部分元素倒序遍历
for item in arrayStr[1...5].reversed() {
    print(item)
}

//方法3：根据索引倒序遍历
for index in (0...(arrayStr.count - 1)).reversed() {
    print(arrayStr[index])
}

//方法4:初始化数组并倒序遍历
for item in Array(1...10).reversed() {
    print(item)
}

//方法4:初始化数组并倒序遍历
for item in Array(1...10).reversed() {
    print(item)
}

//方法5：stride函数
//from，to，by 最后一个值是 >(或<) to的值
//from，through，by 最后一个值是 >=(或<=) through的值
for index in stride(from: arrayStr.count - 1, through: 0,by: -1 )
{
     print(arrayStr[index])
}

 倒序遍历集合

let arrayStr:Set<String> = ["s","t","r","e","n","g"]
//按照字母排序倒序输出
for item in arrayStr.sorted().reversed() {
    print("\(item) ", terminator: "")
}
//Print "t s r n g e" 

倒序遍历字典（可单独遍历键、值、或键值）

var direc: [Int: String] =  [0:"s",1:"t",2:"r",3:"e",4:"n",5:"g"]
//按键值对倒序遍历
for (num, char) in direc.sorted(by: <).reversed() {
    print("\(num): \(char)")
}