题目：Reverse Words in a String
Given an input string s, reverse the string word by word. For example, given s = “the sky is blue”, return “blue is sky the”.
Q: What constitutes a word? A: A sequence of non-space characters constitutes a word.
Q: Does tab or newline character count as space characters? A: Assume the input does not contain any tabs or newline characters.
Q: Could the input string contain leading or trailing spaces? A: Yes. However, your reversed string should not contain leading or trailing spaces.
Q: How about multiple spaces between two words? A: Reduce them to a single space in the reversed string.