How to remember in-order traversal and pre-order traversal in an easy and unforgettable way?

Question

Binary Tree traversal such as preorder traversal, inorder traversal, postorder traversal, and level order traversal is commonly interviewed by many IT companies.

It confuses me to remember the iterative implementation of pre-order traversal and inorder traversal.

Here are the problems from leetcode.

https://leetcode.com/problems/binary-tree-inorder-traversal/

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

Answer 1

1. preorder traversal:

We walk the graph, from top going counter-clockwise. Shout every time we pass the LEFT of a node.

2. inorder traversal:

We walk the graph, from top going counter-clockwise. Shout every time Shout when you cross the bottom.

3. post-order traversal

We walk the graph, from top going counter-clockwise. Shout every time Shout when you cross the right

If you want to see more recursive and iterative implementation details, please read the following post