Today I have done leetcode's September LeetCoding Challenge with cpp.

September LeetCoding Challenge 7

Description

Construct String from Binary Tree

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.

Example 1:

Input: root = [1,2,3,4]
Output: "1(2(4))(3)"
Explanation: Originally, it needs to be "1(2(4)())(3()())", but you need to omit all the unnecessary empty parenthesis pairs. And it will be "1(2(4))(3)"

Example 2:

Input: root = [1,2,3,null,4]
Output: "1(2()(4))(3)"
Explanation: Almost the same as the first example, except we cannot omit the first parenthesis pair to break the one-to-one mapping relationship between the input and the output.

Constraints:

• The number of nodes in the tree is in the range [1, 10^4].
• -1000 <= Node.val <= 1000

Solution

class Solution {
public:
  string tree2str(TreeNode* root) {
    if(!root) return "";
    auto current = to_string(root->val);
    if(root->left || root->right) current += "(" + tree2str(root->left) + ")";
    if(root->right) current += "(" + tree2str(root->right) + ")";
    return current;
  }
};

// Accepted
// 160/160 cases passed (53 ms)
// Your runtime beats 25.89 % of cpp submissions
// Your memory usage beats 23.79 % of cpp submissions (53.9 MB)