Merge pull request #2726 from QinWeijia111/master

Update 0151.翻转字符串里的单词.md

problems/0151.翻转字符串里的单词.md

@@ -475,7 +475,45 @@ class Solution:
         words = words[::-1] # 反转单词
         return ' '.join(words) #列表转换成字符串
 ```
+(版本四) 将字符串转换为列表后，使用双指针去除空格
+```python
+class Solution:
+    def single_reverse(self, s, start: int, end: int):
+        while start < end:
+            s[start], s[end] = s[end], s[start]
+            start += 1
+            end -= 1
 
+    def reverseWords(self, s: str) -> str:
+        result = ""
+        fast = 0
+        # 1. 首先将原字符串反转并且除掉空格, 并且加入到新的字符串当中
+        # 由于Python字符串的不可变性，因此只能转换为列表进行处理
+        s = list(s)
+        s.reverse()
+        while fast < len(s):
+            if s[fast] != " ":
+                if len(result) != 0:
+                    result += " "
+                while s[fast] != " " and fast < len(s):
+                    result += s[fast]
+                    fast += 1
+            else:
+                fast += 1
+        # 2.其次将每个单词进行翻转操作
+        slow = 0
+        fast = 0
+        result = list(result)
+        while fast <= len(result):
+            if fast == len(result) or result[fast] == " ":
+                self.single_reverse(result, slow, fast - 1)
+                slow = fast + 1
+                fast += 1
+            else:
+                fast += 1
+
+        return "".join(result)
+```
 ### Go：
 
 版本一：