老师， 函数式编程和链式编程看的挺像， 有什么区别吗

let source = "Hello world" let target = ["a","e","i","o","u"] let firstOrders = target.map { (character) -> Int? in let index = source.firstIndex(where: { String($0) == character }) return index?.utf16Offset(in: source) } print(zip(target, firstOrders.compactMap({$0 ?? -1})).map({$0})) 感觉还是不够简明扼要

let source = "Hello World" let target: [Character] = ["a", "e", "i", "o", "u"] print(zip(0..<source.count, source).first {target.contains($1)}?.0)

let source = "Hello world" let target: [Character] = ["a","e","i","o","u"] print(source.prefix{!target.contains($0)}.count)

通过第二种方式，岂不是时间复杂度更高了？

zip(0..., "hello world").filter{ ["a", "e", "i", "o", "u"].contains(String($1)) }.first?.0

这个算法里面哪句是给wordDict的key赋值的呢 没发现呀 请指教～

func wordFreq(words:String) -> [String: Int] { var wordDict:[String: Int] = [:] let wordList = words.split(separator: " ") print("wordDict:\(wordDict)") for word in wordList { let lowerCaseWord = word.lowercased() if !NON_WORDS.contains(lowerCaseWord) { if let count = wordDict[lowerCaseWord]{ wordDict[lowerCaseWord] = count + 1 }else{ wordDict[lowerCaseWord] = 1 } } } print("wordDict:\(wordDict)") return wordDict; }

let source = "Hello World" let target: [Character] = ["a", "e", "i", "o", "u"] zip(0..<source.count, source).forEach { if target.contains($0.1) { print($0.0) } }

let source = "Hello world" var target: [Character] = ["a","e","i","o","u"] let result = zip([Character](source.map { $0 }),0 ..< source.count).filter { (char,index) -> Bool in //firstIndex表示已经尝试在target查找char的第一次出现的元素下标了 guard let currentIndex = target.firstIndex(of: char) else { //false时，即target中不包含此Character元素，则此时的char与index不会在新的集合中出现 return false } //发现元素下标后将target中已匹配的元素剔除掉，因为已经找到了，后续的char没必要再找了，不去处会被source重复的char覆盖掉下标 _ = target.remove(at: currentIndex) return true } print(result)