ISRO CSE 2020 | Question: 23

Question

The post-order traversal of binary tree is $\text{ACEDBHIGF}$. The pre-order traversal is

• A. $\text{A B C D E F G H I}$
• B. $\text{F B A D C E G I H}$
• C. $\text{F A B C D E G H I}$
• D. $\text{A B D C E F G I H}$

Comments

Watch this lecture to understand the concept behind this question:

https://youtu.be/5lWJpTEnyow?si=WT4ptxhTd_Kq8SOL

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ASCII VALUE SE BHI KER SAKTE HAI ..

 

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Ans here we analyzed option b and reverse engineered the solution

 

Answer 1

You cannot create a unique tree with post and pre-order traversal you need to have either inorder with preorder or postorder this question seems ambiguous , if it would have been Binary search tree then inorder is sorted sequence and tree is possible but here only binary tree is given.

Comments

You cannot create a unique tree with post and pre-order traversal 

Yes U can given that the tree is $FULL$. But here there is no mention of such thing. So wrong question

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by seeig last element F we can eleminate a and d  now if try to make C as anwer we can not do it so b is right answer 

why C is wrong ?

post = ACEDBHIGF

pre  = F A B C D E G H I  ( option C) 

root is F 

if we put A as right child of F then last 2 element in post order will be AF which is wrong 

if we put A as left child of F then we can not make B as descendent of A because sequence will not start from A in that case now we have to put B as right child of F this is also wrong  bacause last 2 element in post order will be BF which is wrong

 

question is not wrong try with this way ISRO people have made a good question 

Answer 2

The option which might be correct are b,c

Explanation:

 

 

 

 

 

 

 

 

 

 

 

 

 

We can definitely say that the root is F. A can never be the root. While out of option B and C one can't say correctly which would be a preorder for the given postorder. In order to find the preorder, we have to find all the possible trees.

So B or C or None of the options would be correct

Answer 3

it may be answer c-because here in post-order(left right root) leftmost element is A and at last root element is given as F and as per preorder (root left right) so first element must be F and then C(because it is leftmost element in post-order).

Answer 4

You cannot find pre-order traversal using post-order traversal only. I think you wrote a wrong question. It must be binary search tree then only we can find the post order traversal.

Comments

There were many wrong questions in ISRO this year. We have copied those questions directly. Please read the comments before writing your answers.

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yes, we can becoz we know inorder, which is sorted sequence in bsearch tree

Answer 5

Watch this lecture to understand the concept behind this question:

https://youtu.be/5lWJpTEnyow?si=WT4ptxhTd_Kq8SOL

Answer 6

Here we analysed option b and and reverse engineered the solution