Codec

class Codec {
public:
    // ---------- SERIALIZE ----------
    void serializeHelper(TreeNode* root, string &res) {
        if (!root) {
            res += "null,";
            return;
        }
        res += to_string(root->val) + ",";
        serializeHelper(root->left, res);
        serializeHelper(root->right, res);
    }

    string serialize(TreeNode* root) {
        string res;
        serializeHelper(root, res);
        return res;
    }

    // ---------- DESERIALIZE ----------
    TreeNode* deserializeHelper(queue<string> &q) {
        string val = q.front();
        q.pop();

        if (val == "null") return nullptr;

        TreeNode* node = new TreeNode(stoi(val));
        node->left = deserializeHelper(q);
        node->right = deserializeHelper(q);
        return node;
    }

    TreeNode* deserialize(string data) {
        if (data.empty()) return nullptr;

        queue<string> q;
        string temp;

        for (char c : data) {
            if (c == ',') {
                q.push(temp);
                temp.clear();
            } else {
                temp += c;
            }
        }

        return deserializeHelper(q);
    }
};