Iterative Postorder traversal of binary tree using one stack

Postorder traversal of binary tree using one stack.

[santhosh]

I almost got the logic while thinking of the problem. I couldn't think of that inner while loop to break the loop when we are done with all the lefts. Though I could understand your initial explanation, its little tough to match the same with the code. Thanks for the great explanation!!.

[uditgaba]

Thanks for the explanation! You are saving a lot of time for me. Instead of reading articles or reading codes sometimes, i can simply watch your video . I implemented the code on my own after this video .

Code (Java):-
public static void root)
{
Stack<TreeNode> s = new Stack<>();
TreeNode curr = root;
while(curr != null || !s.isEmpty())
{
while(curr != null)
{
s.push(curr);
curr = curr.left;
}

if(!s.isEmpty())
{
//check is stack top has right child
if(s.peek().right != null)
{
= s.peek().right;
}
else
{
temp = s.pop();
");
> 0 && s.peek().right == temp)

= s.pop();
");

}

}
}

[ghostpieces]

Tushar, this was an amazing visual walkthrough followed by a brilliant code walkthrough. Thanks for taking the time to share :)

[meghnasrivastava]

Best explanation, I have watched so far!

[kiratsaluja]

almost got the logic and was stuck at how to check if right is already visited or not. This explains it bang on. Thank u

[vvwu]

Thank you, better than the other explanations I have watched or read.

[yelururao]

super explanation..thanks for it..please do more videos on BST, AVL and red-black tree

[mingxiao]

Clear and intuitive explanation! Thank you Tushar.

[shreyasingh-snbs]

Thank you for making learning so much easier :)

[sureshiva]

straigh forward way ....nice....instead of using previous variable or skip counts....this looks clean

[sameer_sah]

Great walkthrough. Only thing I want to point out is offer and poll are methods of queue API. We should be using push and pop of stack API.

[TwinbeeUK]

Possibly the clearest iterative postorder traversal of trees shown on Youtube! Will this technique of using one stack work if there are 3 or more child nodes for each parent, or would a two-stack solution be needed then?

[karthickm]

Great Video Tushar. In your code, you used, Stack<TreeNode> stack = new LinkedList<>().. Is this correct?

[shivamdixit]

exceptional explanation.... The algo explanation was so good, that i could code it just by looking halfway through the off to the amazing work :)

[JangBahadur]

Awsome tutorial. well explained. Helped me a lot . Thank you Tushar.

[utkarshdwivedi]

A quick question :: you used or in the while condition instead of using and so, whenever the curr will be null the loop will break, without giving the correct output. This thing kind of contradicts with your algorithm.

[chenboxie]

Thank you Tushar, very clear. Understand better now.

[abhinav_]

This iterative traversal has been messing up my mind for long, not anymore.👍

[jbs]

Thank you this was very helpful. Given that space and time complexity are the same using a single stack vs two stacks (please, correct me if I'm wrong), are there any advantages/disadvantages for using a single stack vs two stacks?

[SonGoku-epwj]

dude you're a legend . thank you !