翻转单词顺序列

class Solution {
public:
    //void swap()
    
    void Reversesub(string &str,int a,int b){
        while(a<b)
            swap(str[a++],str[b--]);
    }
    
    string ReverseSentence(string str) {
        int n=str.size();
        Reversesub(str,0,n-1);
        
        int i=0;
        int a=0,b=0;
        while(i<n) {
            while(i<n && str[i]==‘ ‘)
                i++;
            a=b=i;
            while(i<n && str[i]!=‘ ‘) {
                i++;
                b++;
            }
            Reversesub(str,a,b-1);
        }
        return str;
    }
};

class Solution {
public:
void ReverseWord(string &str, int s, int e)
    {
        while(s < e)
            swap(str[s++], str[e--]);
    }
 
    string ReverseSentence(string str) {
        ReverseWord(str, 0, str.size() - 1); //先整体翻转
        int s = 0, e = 0;
        int i = 0;
        while(i < str.size())
        {
            while(i < str.size() && str[i] == ‘ ‘) //空格跳过
                i++;
            e = s = i; //记录单词的第一个字符的位置
            while(i < str.size() && str[i] != ‘ ‘) //不是空格 找单词最后一个字符的位置
            {
                i++;
                e++;
            }
            ReverseWord(str, s, e - 1); //局部翻转
         }
        return str;
    }
};