LeetCode 151 Reverse Words in a String 解题思路和python代码

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"。

class Solution(object):
    def reverseWords(self, s):
        """
        :type s: str
        :rtype: str
        """
        words = s.strip().split()
        reverse_words = words[::-1]
        return ' '.join(reverse_words)