L11. Iterative Postorder Traversal using 2 Stack | C++ | Java | Binary Tree

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[takeUforward]

Hi, hope you are well.


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[codermal]

We can also see it as preorder-> root left right
swap left, right -> root right left
reverse -> left right root
So in first stack we apply pre-order traversal code, and 2 stack is to reverse it, basically we need 2 stack as we can't move from child to parent in tree

[harshitmalhotra]

This year's only video I have watched at 0.5x.

[SaurabhSingh-nvjj]

we can also use the ans vector which we are going to return as the second stack, but in the end we will have to reverse the vector before returning it.

[_jamkhandedattatray]

i shocked when i played this video at 1.75x speed, after read out description I understand what actually happened😂. Anyway but lec is awsome

[JayPanchal]

Understood the concept first and then wrote the code on my own and later found out that it is exactly same as in the video

got confidence....

[theSeniorSDE]

Striver, had to slow down the video speed to understand it better. 😂
Completed this as well.
Steps :
1. initial config : Take the root and put it in the 1st stack.
2. Now, take the top from the 1st stack and put it into the 2nd stack
3. After that, if the top in 2nd stack has left → add it in 1st stack. And if the top in 2nd stack has right → add it in the 1st stack.
4. Now again, take the top from the 1st stack and put it into the 2nd stack. Repeat step 2 & 3 untill 1st stack is empty.
5. Pop the element from the 2nd stack and print.

[takeUforward]

Please likeeee, shareeee and :) Also follow me at Insta: Striver_79

Please watch it at 0.5x or 0.75x, I mistakenly uploded at 2x 🥺

[sahilrao]

only this video i watched at normal speed, else i watch at 2x.

[mohit]

You can make everyone understand in 2x too .. that's the quality in you.. Great man!

[DevanshuAugusty]

what is the intution behind this solution...you are directly junmping to the solution

[tanishq]

I was not at all able to come up with this, I hardly give up on problems, this was impossible for me to think fr!

[omi_iitb]

Intutuion here is that if we observe the sequence, then stack 1 just holds the left and then right valuees just to make sure all right thing done first and then left
stack 2 just holds the root immediately so that it will come at the end and then right which was processed by stack 1 will store and then left

[Rebantaprat]

Striver what is the intuition for using 2 stack 🤔?

[valiz]

explanation is so beautiful, so elegant, just looking like a wow

[kingmysterio]

Can't believe on myself that I was able to crack the code of this one in one stack all by myself without any syntax errors! Thanks Striver

[iamsalonitayal]

I was already watching ur vids at 1.5x . But here:-) for a moment I thought my mind was processing the content slowly. lol. Anyways awesome lectures.

[nandkishor]

hello sir this series is really great. I tried many series on the youtube but your's one is best thank you so much.

[letsrock]

Rather than taking a stack we can save that in the resultant vector and then reverse it in the end We can save some space

[namanchhabra]

In Stack 1 we make
ROOT RIGHT LEFT ( like we did in preorder -> root left right )
Stack2 is used for reverse : -
if we reverse the Stack1 it will give Postorder which is LEFT RIGHT ROOT