Leetcode:Reverse Words in a String

 1 class Solution {
 2 public:
 3     void reverseWords(string &s) {
 4         stack<string> rec;
 5         if(s.empty()) return;
 6         //这里有这个trick,在最后加一个标志字符，象征结束，免得还要在后面循环结束后，看是否还有
 7         //单词没有加入stack中,常用trick
 8         s = s+" ";
 9         string onec;
10         int startind = -1;
11         for(int i=0;i<s.size();i++)
12         {
13             if(s[i]==‘ ‘ && startind==-1) continue;
14             else if(s[i]==‘ ‘){
15                 onec.assign(s.begin()+startind,s.begin()+i);
16                 rec.push(onec);
17                 onec.clear();
18                 startind = -1;
19                 continue;
20             }
21             else if (startind==-1) startind=i;
22             
23         }
24         s="";
25         //必须判断rec是否为空，否则会runtime error，因为后面的删除操作
26         if(rec.empty()) return;
27         while(!rec.empty())
28         {
29             s = s+ rec.top()+" ";
30             rec.pop();
31         }
32         s.erase(s.end()-1);
33         
34     }
35 };