LeetCode--Reverse Words in a String

class Solution {
public:
void reverseWords(string &s) {
int len = s.length();
if(len == 0)
return;
vector<string> res;
int i = 0;
int j = len-1;
//去掉收尾的空格
while(i < len && s[i] == ' ')
++i;
while(j >= 0 && s[j] == ' ')
--j;
int k = i;//寻找一个单词
while(i <= j)
{
k = i;
while(i<=j && s[i]!=' ')
{
++i;
}
res.push_back(s.substr(k,i-k));
while(s[i]==' ' && i<=j)
++i;
}
if(res.empty())
{
s = "";
return;
}
reverse(res.begin(),res.end());
string m = res[0];
for(int i=1;i<res.size();i++){
m+=" ";
m+=res[i];
}
s=m;
}
};