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Editorial Team
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Asked: 2026-05-26T19:21:01+00:00

I have a binary tree, and pre-order traversal. Here is my tree. 15 /

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I have a binary tree, and pre-order traversal.
Here is my tree. 

      15
     / \
   10   23
   /\   /\
  5 12 20 30
    /     /
   11    25
          \
          27

so result of pre-order : 15 10 5 12 11 23 20 30 25 27. It’s OK

Than I delete 5,12 and 23 elements

Should I get this

          15
         / \
       10   27
        \   /\
        11 20 30
               \
               25

Result:15 10 11 27 20 30 25

or this?

      15
     / \
   10   25
    \   /\
    11 20 30
          /
         27

Result: 15 10 11 25 20 30 27

P.S I get 2nd case. If it isn’t right, what is wrong with deletion?

UPD: SO the second updated variant is right?

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1 Answer

  1. Editorial Team

    Your 2nd case is almost right. 27 would be a left node of 30. When deleting a top node of a (sub)tree, you can either replace that node with the right-most node of the left branch or the left-most node of the right branch. In this case, you’ve replaced 30 with the left-most value of the right branch, which is 25. You’d have to perform this recursively as 25 has branches of its own. Once your target node to delete becomes a leaf, delete it.

    First step:

          15
     / \
   10   25
    \   /\
    11 20 30
          /
         23
          \
           27

    Second step:

          15
     / \
   10   25
    \   /\
    11 20 30
          /
         27
        / 
       23

    Third (deletion):

          15
     / \
   10   25
    \   /\
    11 20 30
          /
         27
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