Source: cirosantilli/iterative-in-order
= Iterative in-order
This is a bit harder than <iterative pre-order>: now we have to check if there is a left or right element or not:
* (START) push current
* if there is left:
* move left
* else:
* (ELSE) pop
* visit
* if there is right
* move right
* GOTO START
* else:
* GOTO ELSE
The control flow can be slightly simplified if we allow NULLs: https://www.geeksforgeeks.org/inorder-tree-traversal-without-recursion/