Question Link : https://leetcode.com/problems/binary-tree-preorder-traversal/

Difficulty: Easy

Premium: False

Question

Given the root of a binary tree, return the preorder traversal of its nodes' values.   Example 1:

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

Example 2:

Input: root = [1,2,3,4,5,null …

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