[Lintcode]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".

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.

class Solution {public:    /**     * @param s : A string     * @return : A string     */    string reverseWords(string s) {        // write your code here        string res="";        int len=s.size();        int start=0;        while(start<len) {            while(s[start]==' ')                 start++;            if(start>=len) break; //注意后置0            int index=-1;            index=s.find(" ",start);            string tmp;            if(index==-1) index=len;            tmp=s.substr(start,index-start);            if(res.size()==0) res=tmp;            else res=tmp+" "+res;            start=index+1;        }        return res;    }};