GATE CS 2026 Set 1 — Question 62
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Programming & Data Structures → Trees → Binary Search Trees
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Question
The following sequence corresponds to the preorder traversal of a binary search tree :50, 25, 13, 40, 30, 47, 75, 60, 70, 80, 77The position of the element 60 in the postorder traversal of is ______. (answer in integer)Note: The position begins with 1.
Correct answer
7 to 7
Solution
To find the postorder traversal from the preorder traversal of a Binary Search Tree (BST):
Inorder:
1.Identify the Inorder Traversal: The inorder traversal of a BST is the elements of the preorder traversal sorted in ascending order.
Preorder: Inorder:
2.Construct the BST:
- The first element in preorder is the root: 50.
- Elements smaller than 50 are in the left subtree: .
- Elements larger than 50 are in the right subtree: .
- Left of 25:
- Right of 25: (Root 40)
- Left of 40:
- Right of 40:
- Left of 75: (Root 60)
- Right of 60:
- Right of 75: (Root 80)
- Left of 80:
- Postorder of Left Subtree:
- Postorder of Right Subtree:
- Full Postorder:
- 1st: 13
- 2nd: 30
- 3rd: 47
- 4th: 40
- 5th: 25
- 6th: 70
- 7th: 60
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