482. License Key Formatting

 static int wing=[]()
 {
     std::ios::sync_with_stdio(false);
     cin.tie(NULL);
     return ;
 }();

 class Solution
 {
 public:
     string licenseKeyFormatting(string S, int K)
     {
         int len=S.length();
         int count=;
         string res;
         for(int i=len-;i>=;i--)
         {
             char c=toupper(S[i]);
             if(c=='-')
                 continue;
             res.push_back(c);
             count++;
             if(count==K)
             {
                 res.push_back('-');
                 count=;
             }
         }
         if(res.back()=='-')
             res.pop_back();
         reverse(res.begin(),res.end());
         return res;
     }
 };

从后往前扫描，问题不大