Recall & Review
beginner
What is the main goal of the Two Sum problem in a Binary Search Tree (BST)?
To find if there exist two nodes in the BST such that their values add up to a given target sum.
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intermediate
Why is BST property useful in solving the Two Sum problem?
Because BST nodes are ordered, we can use in-order traversal to get sorted values, which helps in efficiently finding pairs that sum to the target.
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beginner
What data structure is commonly used to check for complements when solving Two Sum in BST?
A hash set is used to store visited node values to quickly check if the complement (target - current node value) exists.
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advanced
Explain the two-pointer approach for Two Sum in BST.
Perform in-order traversal to get sorted values, then use two pointers at start and end to find if any two values sum to the target by moving pointers inward based on sum comparison.
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intermediate
What is the time complexity of solving Two Sum in BST using a hash set during traversal?
O(n), where n is the number of nodes, because each node is visited once and hash set operations are O(1) on average.
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What traversal method is best to get sorted node values from a BST?
✗ Incorrect
In-order traversal visits nodes in ascending order for BSTs.
Which data structure helps to check if a complement value exists during Two Sum in BST?
✗ Incorrect
Hash set allows O(1) average time lookup for complements.
If you use two pointers on a sorted array of BST values, what do you do if the sum is less than the target?
✗ Incorrect
Moving the left pointer right increases the sum.
What is the worst-case time complexity of Two Sum in BST using hash set approach?
✗ Incorrect
Each node is visited once, so O(n).
Which of these is NOT a valid approach to solve Two Sum in BST?
✗ Incorrect
Pre-order traversal does not produce sorted values, so it is not suitable for two-pointer approach but can be used with hash set. The question is about valid approaches; pre-order + hash set is valid but less common.
Describe how you would find two nodes in a BST that sum to a target value using a hash set.
Think about storing visited values and checking complements.
You got /6 concepts.
Explain the two-pointer technique to solve Two Sum in BST and why it requires in-order traversal.
Sorting is key to two-pointer method.
You got /7 concepts.