[Swift]遍歷集合類型（數組、集合和字典）

★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★
➤微信公眾號：山青詠芝（shanqingyongzhi）
➤博客園地址：山青詠芝（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 
➤如果鏈接不是山青詠芝的博客園地址，則可能是爬取作者的文章。
➤原文已修改更新！強烈建議點擊原文地址閱讀！支持作者！支持原創！
★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★

Swift提供了三種主要的集合類型，稱為數組，集合和字典，用於存儲值集合。

數組是有序的值集合。

集是唯一值的無序集合。

字典是鍵值關聯的無序集合。

Swift中無法再使用傳統形式的for循環。

//傳統for循環形式不適用於Swift
for（單次表達式;條件表達式;末尾循環體）{中間循環體；}

遍歷數組：可以使用for- in循環遍歷數組中的值。

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

//方法1:根據元素順序遍歷
for item in arrayStr {
    print(item)
}

//方法2:根據部分元素順序遍歷
for item in arrayStr[1...5] {
    print(item)
}

//方法3：根據索引順序遍歷
for index in 0...(arrayStr.count - 1) {
    print(arrayStr[index])
}

//方法4:初始化數組並順序遍歷
for item in Array(1...10) {
    print(item)
}

//方法5：stride函數
//from，to，by 最后一個值是 >(或<) to的值
//from，through，by 最后一個值是 >=(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個值，則可以使用下划線（_）代替變量名來忽略這些值。

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"

遍歷集合：可以使用for- in循環遍歷集合中的值。

 let arrayStr:Set<String> = ["s","t","r","e","n","g"]
//輸出的順序是隨機的
for item in arrayStr {
    print("\(item)")
}

Swift的Set類型沒有定義的順序。要以特定順序迭代集合的值，請使用該sorted()方法，該方法將集合的元素作為使用<運算符排序的數組返回。

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

遍歷字典（可單獨遍歷鍵、值、或鍵值）

可以用字典遍歷鍵值對for- in環。字典中的每個項都作為元組返回，您可以將元組的成員分解為臨時常量或變量，作為迭代的一部分：(key, value),還可以通過訪問字典的鍵keys和values屬性來檢索字典的鍵或值的可迭代集合：

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

//按鍵值對遍歷順序遍歷
for (num, char) in direc.sorted(by: <) {
    print("\(num): \(char)")
}

//按鍵遍歷順序遍歷
for num in direc.keys.sorted(by: <) {
    print("\(num)")
}

//按值遍歷順序遍歷
for char in direc.values {
    print("\(char)")
}

如果您需要使用帶有Array實例的API的字典鍵或值，請使用keys或values屬性初始化新數組：

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

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

Swift的Dictionary類型沒有定義的順序。要按特定順序迭代字典的鍵或值，請sorted()在其keys或values屬性上使用該方法。

倒序遍歷 :reversed() 或 stride函數

Swift中標准庫中方法

//可以用來快速的枚舉數組中的內容，並用元組(index, value)接收
public func enumerated() -> EnumeratedSequence<Array<Element>>

//可以倒敘數組內容
public func reversed() -> ReversedRandomAccessCollection<Array<Element>>

當兩者結合使用用到索引時需要注意

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

//索引元素值綁定一起倒序遍歷
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") 
*/

//只元素值倒序遍歷，原索引不變
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") 
*/

倒序遍歷數組

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

//方法1:根據元素倒序遍歷
for item in arrayStr.reversed() {
    print(item)
}

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

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

//方法4:初始化數組並倒序遍歷
for item in Array(1...10).reversed() {
    print(item)
}

//方法4:初始化數組並倒序遍歷
for item in Array(1...10).reversed() {
    print(item)
}

//方法5：stride函數
//from，to，by 最后一個值是 >(或<) to的值
//from，through，by 最后一個值是 >=(或<=) through的值
for index in stride(from: arrayStr.count - 1, through: 0,by: -1 )
{
     print(arrayStr[index])
}

 倒序遍歷集合

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

倒序遍歷字典（可單獨遍歷鍵、值、或鍵值）

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