整体翻转，再每个单词翻转

class Solution {
public:
    string ReverseSentence(string str) {
        reverse(str.begin(),str.end());
        int i=0,j=0;
        while(i<str.length())
        {
            while(j<str.length()&&str[j]!=' ')j++;
            reverse(str.begin()+i,str.begin()+j);
            i=++j;
        }
        return str;
    }
};

分词然后加起来

class Solution {
public:
    string ReverseSentence(string str) {
        string ans="",temp="";
        for(int i=0;i<str.length();i++)
        {
            if(str[i]==' ')ans=" "+temp+ans,temp="";
            else temp+=str[i];
        }
        ans=temp+ans;
        return ans;
    }
};