[Swift]LeetCode186.翻转字符串中的单词II$ReverseWordsinaStringII

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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?

给定输入字符串，逐字反转字符串。单词被定义为非空格字符序列。

输入字符串不包含前导或后缀空格，并且单词总是由一个空格分隔。

例如，

给定 s = "the sky is blue",

返回 "blue is sky the".。

您能在不分配额外空间的情况下就地完成吗？

 1 class Solution {
 2     func reverseWords(_ s: inout String){
 3         var left:Int = 0
 4         for i in 0...s.count
 5         {
 6             if i == s.count || s[i] == " "
 7             {
 8                 reverse(&s, left, i - 1)
 9                 left = i + 1
10             }
11         }
12         reverse(&s, 0, s.count - 1)
13     }
14     
15     func reverse(_ s: inout String,_ left:Int,_ right:Int)
16     {
17         var left = left
18         var right = right
19         while (left < right)
20         {
21             var t:Character = s[left]
22             s[left] = s[right]
23             s[right] = t
24             left += 1
25             right -= 1
26         }
27     }
28 }
29 
30 extension String {        
31     //subscript函数可以检索数组中的值
32     //直接按照索引方式截取指定索引的字符
33     subscript (_ i: Int) -> Character {
34         //读取字符
35         get {return self[index(startIndex, offsetBy: i)]}
36         
37         //修改字符
38         set
39         {
40             var str:String = self
41             var index = str.index(startIndex, offsetBy: i)
42             str.remove(at: index)
43             str.insert(newValue, at: index)
44             self = str
45         }
46     }
47 }