Reverse Words in a String

Question

• leetcode: (151) Reverse Words in a String
• lintcode: (53) Reverse Words in a String

Given an input string, reverse the string word by word.

For example,
Given s = "the sky is blue",
return "blue is sky the".

Example
Clarification

- What constitutes a word?
A sequence of non-space characters constitutes a word.

- Could the input string contain leading or trailing spaces?
Yes. However, your reversed string should not contain leading or trailing spaces.

- How about multiple spaces between two words?
Reduce them to a single space in the reversed string.

题解

1. 由第一个提问可知：题中只有空格字符和非空格字符之分，因此空格字符应为其一关键突破口。
2. 由第二个提问可知：输入的前导空格或者尾随空格在反转后应去掉。
3. 由第三个提问可知：两个单词间的多个空格字符应合并为一个或删除掉。

首先找到各个单词(以空格隔开)，根据题目要求，单词应从后往前依次放入。正向取出比较麻烦，因此可尝试采用逆向思维——先将输入字符串数组中的单词从后往前逆序取出，取出单词后即翻转并append至新字符串数组。在append之前加入空格即可。

• reference

class Solution:
    # @param s, a string
    # @return a string
    def reverseWords(self, s):
        return " ".join(s.split()[::-1])