[LintCode] Reverse Words in a String 翻轉字元串中的單詞

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

For example,

Given s = "<code>the sky is blue</code>",

return "<code>blue is sky the</code>".

Have you met this question in a real interview? 

Yes

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.

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