151. Reverse Words in a String

class Solution {
public:
    string reverseWords(string s) {
        s.insert(0," ");
        string res="";
        int len = s.length();
        int left=len-1,right=len-1;
        while(right>=0){
            
            while(right>=0&&s[right]==' ')
                right--;
            
            if(right<0)
                break;
            left=right;
            
            while(s[left]!=' ')
                left--;
            
            for(int i=left+1;i<=right;i++)
                res.push_back(s[i]);
            
            res.push_back(' ');
            right=left;
        }
        if(res.length()!=0)
            res.pop_back();
        return res;
    }
};

从后往前扫，给原字符串前面加一个空格，就可以统一处理了