题目：
Given an input string s, reverse the order of the words.
A word is defined as a sequence of non-space characters. The words in s will be separated by at least one space.
Return a string of the words in reverse order concatenated by a single space.
Note that s may contain leading or trailing spaces or multiple spaces between two words. The returned string should only have a single space separating the words. Do not include any extra spaces.
Example 1:
Input: s = "the sky is blue"
Output: "blue is sky the"
Example 2:
Input: s = " hello world "
Output: "world hello"
Explanation: Your reversed string should not contain leading or trailing spaces.
Example 3:
Input: s = "a good example"
Output: "example good a"
Explanation: You need to reduce multiple spaces between two words to a single space in the reversed string.
Constraints:
1 <= s.length <= 104
s contains English letters (upper-case and lower-case), digits, and spaces ' '.
There is at least one word in s.
Follow-up: If the string data type is mutable in your language, can you solve it in-place with O(1) extra space?
解题思路：
首先，去掉前后空格。
然后，利用split()将string按空格分割成一个单词list。
接着，反转单词list。
最后，将反转后的单词list用空格连接起来。
例子：
" hello world "，先去掉前后空格得到 ["hello", "world"]，反转后是 ["world", "hello"]，输出 "world hello"。
python
class Solution(object):
def reverseWords(self, s):
"""
:type s: str
:rtype: str
"""
words = s.strip().split()
reverse_words = words[::-1]
return ' '.join(reverse_words)