这道题有In place and non In place两种做法。in place的做法是，先把所有单词逐一翻转，再最后翻转整个句子(151由于空格，需要extra check)

In place:

class Solution {
public:
    void reverseWords(string &s) {
        if(s.empty()) return;
        int left = 0;
        for(int i=0; i<=s.length(); i++){
            if(i == s.length() || s[i] == ' '){
                myReverse(s, left, i-1);
                left = i+1;
            }
        }
        reverse(s.begin(), s.end());
    }
    
    void myReverse(string &s, int start, int end){
        while(start < end){
            swap(s[start], s[end]);
            start++; end--;
        }
    }
};

In place with character array:

class Solution {
public:
    
    void reverse_util(vector<char>& str, int left, int right) {
        reverse(str.begin() + left, str.begin() + right);
    }
    
    void reverseWords(vector<char>& str) {
        if(str.empty()) {
            return;
        }

        int left = 0;
        for(int i=0; i<=str.size(); i++) {
            if(i == str.size() || str[i] == ' '){
                reverse_util(str, left, i);
                left = i+1;
            }
        }
        reverse(str.begin(), str.end());
    }
};

With extra memory:

class Solution {
public:
    void reverseWords(string &s) {
        if(s.empty()) return;
        int cur_len = 0;
        string ret = "";
        for(int i=s.length()-1; i>=0; i--){
            if(s[i] == ' '){
                if(cur_len == 0) continue;
                else{
                    string word = s.substr(i+1, cur_len);
                    ret += word;
                    ret += ' ';
                    cur_len = 0;
                }
            }else{
                cur_len++;
            }
        }
        if(cur_len > 0) ret += s.substr(0, cur_len);
        s = ret;
        while(s.length() > 1 && s[0] == ' ') s.erase(0, 1);
        while(s.back() == ' ') s.pop_back();
    }
};