Level: Medium
Question
Example 1:
Given the root of a binary tree, return the preorder traversal of its nodes' values.
Input: root = [1,null,2,3]
Output: [1,2,3]Example 2:
Input: root = []
Output: []Example 3:
Input: root = [1]
Output: [1]Example 4:
Input: root = [1,2]
Output: [1,2]Example 5:
Input: root = [1,null,2]
Output: [1,2]Constraints:
- The number of nodes in the tree is in the range
[0, 100]. -100 <= Node.val <= 100
Solutions
Thought 1 — Recursive
It’s an easy solution. No explanation needed.
Thought 2 — Iterative
Using a stack to complete implementation. Be aware that put the right node in front of the left node because of Fist-In-Last-Out.
Happy programming!
