231209 LeetCode 문제 풀이

606. Construct String from Binary Tree

https://leetcode.com/problems/construct-string-from-binary-tree/?envType=daily-question&envId=2023-12-08

 

1) 문제 설명

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.

 

2) 제한 사항

• The number of nodes in the tree is in the range [1, 104].
• -1000 <= Node.val <= 1000

 

3) 도전 과제

X

 

4) 풀이

아직 재귀를 이해하고 구현하지 못하겠어서, 우선은 다른 사람의 해답 사용.

 

재귀 관련 문제들을 풀어보면서 익혀야 할 것 같음.

 

5) 소스 코드 및 결과

X

 

6) 다른 사람의 풀이

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> res = new ArrayList<>();
        helper(root, res);
        return res;
    }

    public void helper(TreeNode root, List<Integer> res) {
        if (root != null) {
            helper(root.left, res);
            res.add(root.val);
            helper(root.right, res);
        }
    }
}