Binary Tree Preorder Traversal

Difficulty

Easy

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]

Example 2:

Input: root = [1,2,3,4,5,null,8,null,null,6,7,9]
Output: [1,2,4,5,6,7,3,8,9]

Example 3:

Input: root = []
Output: []

Example 4:

Input: root = [1]
Output: [1]

Constraints:

The number of nodes in the tree is in the range [0, 100].
-100 <= Node.val <= 100

Link

Binary Tree Preorder Traversal

Solution

Solution implements both recursive and iterative approach, where the second utilizes stack to traverse the tree.