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".

class Solution {
public:
    void reverseWords(string &s) {
        reverseWords1(s);
    }
    
     void reverseWords1(string &s) {
        istringstream is(s);
        string word;
        vector<string> vs;
        while (is >> word) vs.push_back(word);
        reverse(vs.begin(), vs.end());
        ostringstream os;
        for (int i = 0; i < vs.size(); i++) {
            if (i != 0) os << " ";
            os << vs[i];
        }
        s = os.str();
    }

    void reverseWords2(string &s) {
        string res;
        int i = s.size() - 1;
        while (i >= 0) {
            while (i >= 0 && s[i] == ' ') i--;
            if (i < 0) break;
            string tmp;
            while (i >= 0 && s[i] != ' ') tmp.push_back(s[i--]);
            reverse(tmp.begin(), tmp.end());
            if (!res.empty()) res.push_back(' ');
            res.append(tmp);
        }
        s = res;
    }
};