class Solution {
public:
    string decodeString(string s) {
        stack<int> repeat;
        stack<string> patterns;
        string res;
        int i = 0;
        while (i < s.length())
        {
          string cur;
          while (i < s.length() && isalpha(s[i]))
          {
            cur += s[i];
          }
          if (i < s.length() && s[i] == ‘]’) ++i;

          if (!repeat.empty()) patterns.push(cur);
          else res += cur;

          if (s[i] - ‘0’ < 9 && s[i] - ‘0’ >=0)
          {
            int step =  s.find(i, ‘[’);
            repeat.push(atoi(s.substr(i, step);
            i = step + 1;
          }
        }
    }
};