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

For example,

Given s = "the sky is blue",

return "blue is sky the".

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.

思路：从头往后扫描字符串，从第一个开始不是空格算起。将单词放入temp中，直到遇到空格，作如下处理，将单词放入result中去，接下来再有单词可以放到上一个单词的前面，另加空格。如此反复，就可以将单词与单词为单位反转了。

class Solution {public:    void reverseWords(string &s) {        int nLen=s.size();        if(nLen<=0)            return;        string temp,result;        int index=0;        while(s[index]==' ')            index++;        for(int i=index;i