翻转单词顺序列

 1 class Solution {
 2 public:
 3     string ReverseSentence(string str) {
 4         if(str.length() < 1)
 5             return str;
 6         bool sp = 1;
 7         for (int i = 0 ;i < str.length() ; ++i)
 8         {
 9             if(str[i] != ‘ ‘)
10             {
11                 sp = 0;
12                 break;
13             }
14         }
15         if(sp)
16         {
17             return str;
18         }
19         stringstream ss;
20         ss << str;
21         string stem;
22         stack<string> st;
23         while(ss>>stem)
24         {
25             st.push(stem);
26         }
27         stem = "";
28         bool fir = 1;
29         while(!st.empty())
30         {
31             if (fir)
32             {
33                 fir = 0;
34                 stem += st.top();
35             }
36             else
37             {
38                 stem += " " + st.top();
39             }
40             st.pop();
41         }
42         return stem;
43     }
44 };