10-04每日一题：Leetcode482. 密钥格式化

class Solution {
public:
    string licenseKeyFormatting(string s, int k) {
        string res;
        for (int i = s.size() - 1, cnt = 0; i >= 0; i -- ) {
            if (s[i] != '-') {
                res.push_back(toupper(s[i]));
                cnt ++ ;
                if (cnt % k == 0) res += '-';
            }
        }
        if (res.back() == '-') res.pop_back();
        reverse(res.begin(), res.end());
        return res;
    }
};