/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
 public:
  string tree2str(TreeNode* t) {
    return dfs(t);
  }

 private:
  string dfs(TreeNode* root) {
    if (!root)
      return "";

    const string& rootStr = to_string(root->val);
    if (root->right)
      return rootStr + "(" + dfs(root->left) + ")(" + dfs(root->right) + ")";
    if (root->left)
      return rootStr + "(" + dfs(root->left) + ")";
    return rootStr + "";
  }
};