Description
Given the root of an n-ary tree, return the preorder traversal of its nodes values. Preorder visits the root first, then all children from left to right.
Examples
Input:
root = [1,null,3,2,4,null,5,6]Output:
[1,3,5,6,2,4]Explanation:
Preorder: root, then children.
Input:
root = []Output:
[]Explanation:
Empty tree case: when the root is null/empty, preorder traversal returns an empty array since there are no nodes to visit.
Input:
root = [7,null,2,9,1,8,null,null,6]Output:
[7,2,6,9,1,8]Explanation:
Preorder traversal visits root first (7), then recursively visits each child's subtree from left to right: first child 2 and its child 6, then second child 9, then third child 1, and finally fourth child 8.
Constraints
- •
0 ≤ nodes ≤ 10⁴