Binary Tree Preorder Traversal

Given the root of a binary tree, return the preorder traversal of its nodes’ values.

Class TreeNode:
    val (int)
    left (TreeNode)
    right (TreeNode)

Input Format

First Parameter - TreeNode root

Output Format

Return the array of values of nodes in preorder sequence.

Example 1:

Input: 
    1 null 3 null 5 7 6 null 8
Output: 
    1 3 5 7 8 6

Example 2:

Input:
    15 10 12 13 null 5 null null 14
Output: 
    15 10 13 14 12 5

Constraints

• The number of nodes in the tree is in the range [0, 100].
• -100 <= Node.val <= 100
• Expected Time Complexity: O(n)
• Expected Space Complexity: O(1)