class Solution {
public:

    bool recursion(string seq) {
        if (seq.size() > 1 && seq.front() == '#')
            return false;
        if (seq.size() % 2 == 0)
            return false;
        else if (seq.size() == 1)
            return seq.front() == '#';
        // else if (seq.find("####") != -1)
            // return false;

        bool isFind = false;

        string seq_next;
        int i;
        for (i = 0; i < seq.size() - 2;) {
            if (seq[i+1] == '#' && seq[i+2] == '#' && seq[i] != '#') {
                seq_next += '#';
                i += 3;
                isFind = true;
            }
            else {
                seq_next += seq[i++];
            }
        }

        seq_next += seq.substr(i);

        cout << seq_next << endl;

        return isFind ? recursion(seq_next) : isFind;
    }


    bool isValidSerialization(string preorder) {
        string seq;
        string item;
        stringstream ss(preorder);


        while (std::getline(ss, item, ',')) {
            if (item == "#")
                seq += "#";
            else
                seq += "n";
        }

        stack<char> s;

        int i = 0;
        while (i < seq.size()) {
            if (seq[i] == '#' && seq.empty())
                return false;
            
        }

        return ;
    }
};