[LeetCode/Easy] 144. Binary Tree Preorder Traversal

1. Input

1) TreeNode root

 

2. Output

1) root를 전위순회한 결과를 리스트에 담아 반환

 

3. Constraint

1) root에 있는 노드의 수는 [0, 100]이다.

2) -100 <= Node.val <= 100

 

4. Example

Input: root = [1,null,2,3] -> Output: [1,2,3]

 

5. Code

1) 첫 코드(2023/05/12)

/**
 * 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> preorderTraversal(TreeNode root) {
        List<Integer> pre = new ArrayList<>();
        if(root!=null){
            pre.add(root.val);
            pre.addAll(preorderTraversal(root.left));
            pre.addAll(preorderTraversal(root.right));
        }
        return pre;
    }
}