0606 - Construct String from Binary Tree.cpp

/**
 * 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* root)
    {
        std::string output{std::to_string(root->val)};
        if (root->left)
            output += "(" + tree2str(root->left) + ")";
        if (root->right)
        {
            if (!root->left) output += "()";
            output += "(" + tree2str(root->right) + ")";
        }
        return output;
    }
};