Swift算法實現逐字翻轉字符串的方法示例。本站提示廣大學習愛好者:(Swift算法實現逐字翻轉字符串的方法示例)文章只能為提供參考,不一定能成為您想要的結果。以下是Swift算法實現逐字翻轉字符串的方法示例正文
前言
翻轉字符串在字符串算法中算是比較常見的,而且被很多公司用作筆試題。”逐字翻轉字符串”是翻轉字符串的翻版,也是之前Google的面試題,原題是這樣的:
Given an input string, reverse the string word by word. A word is defined as a sequence of non-space characters. The input string does not contain leading or trailing spaces and the words are always separated by a single space. For example, Given s = "the sky is blue", return "blue is sky the". Could you do it in-place without allocating extra space?
簡而言之就是:”the sky is blue”—>”blue is sky the”
所以,對於本文,要解決的算法是:
逐字翻轉字符串,例如:"the sky is blue"—>"blue is sky the"
接下來看下實現思路和代碼。
實現思路及代碼
既然是字符串翻轉的翻版,我們就可以利用之前翻版字符串的思路去解決就可以了,不過這道題要有兩次翻轉:
第一次翻轉,整體翻轉:”the sky is blue” -> “eulb si yks eht”
第二次翻轉,單詞翻轉:”eulb si yks eht” -> “blue is sky the”
所以,首先可以實現一個可以翻轉局部和全部字符串的算法,傳入字符數組、startIndex 和 endIndex ,其中 startIndex 和 endIndex 分別為要翻轉的字符串的起始下標和結束下標,也就是要翻轉 startIndex 和 endIndex 之間(包含)的字符,代碼如下:
func _reverseStr( _ chars:inout [Character], _ startIndex:Int, _ endIndex:Int){ var startIndex = startIndex var endIndex = endIndex if startIndex <= endIndex { let tempChar = chars[endIndex] chars[endIndex] = chars[startIndex] chars[startIndex] = tempChar startIndex += 1 endIndex -= 1 _reverseStr(&chars,startIndex,endIndex) } }
之後就可以利用上面的算法去完成前面說的兩次翻轉:
func reverseWords(_ str:String) -> String{ var chars = [Character](str.characters) //首先翻轉整個字符串所有字符,"the sky is blue" -> "eulb si yks eht" _reverseStr(&chars,0,chars.count-1) //然後翻轉每個單詞中的字符,"eulb si yks eht" -> "blue is sky the" var startIndex = 0 for endIndex in 0 ..< chars.count { if endIndex == chars.count - 1 || chars[endIndex + 1] == " " { _reverseStr(&chars, startIndex, endIndex) startIndex = endIndex + 2 } } return String(chars) }
完整算法代碼:
//翻轉指定范圍的字符 func _reverseStr( _ chars:inout [Character], _ startIndex:Int, _ endIndex:Int){ var startIndex = startIndex var endIndex = endIndex if startIndex <= endIndex { let tempChar = chars[endIndex] chars[endIndex] = chars[startIndex] chars[startIndex] = tempChar startIndex += 1 endIndex -= 1 _reverseStr(&chars,startIndex,endIndex) } } //逐字翻轉字符串 func reverseWords(_ str:String) -> String{ var chars = [Character](str.characters) //首先翻轉整個字符串所有字符,"the sky is blue" -> "eulb si yks eht" _reverseStr(&chars,0,chars.count-1) //然後翻轉每個單詞中的字符,"eulb si yks eht" -> "blue is sky the" var startIndex = 0 for endIndex in 0 ..< chars.count { if endIndex == chars.count - 1 || chars[endIndex + 1] == " " { _reverseStr(&chars, startIndex, endIndex) startIndex = endIndex + 2 } } return String(chars) } reverseWords("the sky is blue") //return "blue is sky the"
總結
以上就是關於Swift算法實現逐字翻轉字符串的方法,希望本文的內容對大家的學習或者工作能帶來一定的幫助,如果有疑問大家可以留言交流,謝謝大家對的支持。