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The preorder traversal of a binary search tree is $15, 10, 12, 11, 20, 18, 16, 19$. Which one of the following is the postorder traversal of the tree?

  1. $10,11,12,15,16,18,19,20$
  2. $11,12,10,16,19,18,20,15$
  3. $20,19,18,16,15,12,11,10$
  4. $19,16,18,20,11,12,10,15$
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To get the answer quickly, just identify the root element which is by preorder traversal is 15, so A,C cannot be the answer. For the remaining option,given that the tree is BST, the right subtree’s value is greater than the root’s value so D cannot be the answer. So, the answer is B.
Answer:

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