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 whose 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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intermediate
What is a common approach to solve Two Sum in BST using extra space?
Perform an in-order traversal to get a sorted array of node values, then use two pointers (start and end) to find if any two values sum to the target.
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advanced
How can we solve Two Sum in BST without converting it to an array?
Use two iterators: one for the smallest value (in-order) and one for the largest value (reverse in-order), then move them towards each other to find the target sum.
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intermediate
What is the time complexity of the Two Sum in BST solution using in-order traversal and two pointers?
O(n), where n is the number of nodes in the BST, because we visit each node once during traversal and then use two pointers to find the pair.
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What traversal method is commonly used to get sorted values from a BST?
✗ Incorrect
In-order traversal visits BST nodes in ascending order, giving sorted values.
In the Two Sum problem on BST, what data structure helps to check if a complement value exists quickly?
✗ Incorrect
A hash set allows O(1) average time lookup to check if the complement of the current node's value exists.
Which technique uses two pointers to find two numbers that add up to a target in a sorted array?
✗ Incorrect
Two-pointer technique moves pointers from start and end towards each other to find the target sum.
What is the space complexity of the Two Sum in BST solution using in-order traversal and array conversion?
✗ Incorrect
Storing all node values in an array requires O(n) space.
Which of these is NOT a valid approach to solve Two Sum in BST?
✗ Incorrect
Post-order traversal alone does not help efficiently find pairs without extra data structures.
Explain how to solve the Two Sum problem in a BST using in-order traversal and two pointers.
Think about how sorted arrays help find pairs with a target sum.
You got /4 concepts.
Describe the space-optimized approach to find two nodes in a BST that sum to a target without converting the BST to an array.
Imagine walking from smallest and largest values at the same time.
You got /4 concepts.