Construct String from Binary Tree.cpp

/* 
    Solution by Rahul Surana
    
    ***********************************************************


Given the root of a binary tree, construct a string consisting of parenthesis 
and integers from a binary tree with the preorder traversal way, and return it.

Omit all the empty parenthesis pairs that do not affect the one-to-one mapping 
relationship between the string and the original binary tree.


    ***********************************************************
*/

    
/**
 * 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) {
        if(!root) return "()";
        if(!root->left && !root->right) return to_string(root->val);
        return to_string(root->val) + (root->left ? "("+tree2str(root->left)+")":"()") 
                + (root->right ? "("+tree2str(root->right)+")" : "");
    }
};