class Solution
{
public:
    string decodeString(string s)
    {
        stack<char> st;
        string freq = "";
        stack<int> num;
        if (s.size() == 0)
        {
            return s;
        }
        int fr=0;
        for (int i = 0; i < s.size(); i++)
        {
            if (isdigit(s[i]))
            {
                freq.push_back(s[i]);
            }

            if (s[i] != ']' && !isdigit(s[i]))
            {
                st.push(s[i]);
            }
            else if (!st.empty() && s[i] == ']')
            {
                fr = fr +stoi(freq);
                num.push(fr);
                freq = "";
                fr=0;
                string res = "";

                while (st.top() != '[')
                {
                    char ch = st.top();
                    res.push_back(ch);
                    st.pop();
                }
                st.pop(); // To remove '[' form the stack

                reverse(res.begin(), res.end());
                int t = 0;
                t = t + num.top();
                num.pop();
                while (t--)
                {
                    for (int i = 0; i < res.size(); i++)
                    {
                        st.push(res[i]);
                    }
                }
            }
        }
        string str = "";
        while (!st.empty())
        {
            str.push_back(st.top());
            st.pop();
        }
        reverse(str.begin(), str.end());
        return str;
    }
};