(leetcode 1)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".

click to show clarification.

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.

void reverseWords(string &s) {        if(s=="")        return;    int i = s.size()-1,flagL,flagR;    string tmp = "";    for(; i >= 0; i--)    {        while(i >= 0 && ' '== s[i])i--;        flagR = i; //从右开始找到第一个不是 “  ” 的字符位置        while(i >= 0 && ' '!= s[i])i--;        flagL = i+1;//从右向左开始找到第二个不是 “  ” 的字符位置        if(flagL>=0&&flagR>=0)            tmp += s.substr(flagL,flagR-flagL+1)+" ";    }        s = tmp;        if(s.size()>1)            s.erase(s.size()-1,1);    }