Leetcode151 flipping words in strings

Give you a string s , Flip all in the string one by one word .

word Is a string of non whitespace characters .s Use at least one space in the string word Separate .

Please return to a flip s A string in word order and connected by a single space .

explain ：

Input string s It can be in the front 、 Contain extra spaces after or between words .
After flipping, the words should be separated by only one space .
The flipped string should not contain additional spaces .

Example 1：

Input ：s = “the sky is blue”
Output ：“blue is sky the”
Example 2：

Input ：s = " hello world "
Output ：“world hello”
explain ： The input string can contain extra spaces before or after , However, the flipped characters cannot include .
Example 3：

Input ：s = “a good example”
Output ：“example good a”
explain ： If there are extra spaces between two words , Reduce the space between words after flipping to only contain one .
Example 4：

Input ：s = " Bob Loves Alice "
Output ：“Alice Loves Bob”
Example 5：

Input ：s = “Alice does not even like bob”
Output ：“bob like even not does Alice”

python The string of cannot be modified in place , So it can only cost O(n) Extra space to create a list
Time complexity O(n)

class Solution:
    def reverseWords(self, s: str) -> str:
        #  Remove the extra white space characters at the beginning, end and middle of the string 
        s_list = self.trim(s)
        #  Flip strings 
        self.reverse(s_list, 0, len(s_list)-1)
        #  Flip each word 
        self.reverse_words(s_list)
        return ''.join(s_list)
    
    
    def trim(self, s):
        left = 0
        right = len(s) - 1 
        #  Remove the white space character at the beginning of the string 
        while s[left] == ' ':
            left += 1
        #  Remove the white space character at the end of the string 
        while s[right] == ' ':
            right -= 1
        #  Remove extra white space characters between strings 
        output = []
        while left <= right:
            if s[left] == ' ' and output[-1] == ' ':
                left += 1
            else:
                output.append(s[left])
                left += 1
        return output
        
    def reverse(self, s, l, r):
        while l < r:
            s[l], s[r] = s[r], s[l]
            l += 1 
            r -= 1 
            
    def reverse_words(self, s):
        left = 0 
        right = 0
        while right < len(s):
            #  Loop to the end of the word 
            while (right < len(s)) and (s[right] != ' '):
                right += 1
            #  Flip Words 
            self.reverse(s, left, right-1)
            #  to update start, Find the next word 
            left = right + 1 
            right = right + 1