11Reverse words in a sentence

Implement reverseWords(s). It returns the words of the sentence in reverse order, joined by a single space. A word is a run of non-space characters.

reverseWords("the sky is blue"); // "blue is sky the"
reverseWords("  hello world  "); // "world hello"
reverseWords("a good   example"); // "example good a"

Requirements

• Remove leading and trailing spaces.
• Collapse several spaces between words into one.
• Keep each word itself unchanged, including punctuation.
• Solve it in O(n) time.