How do you calculate the lowest common ancestor in a binary search tree?
This problem evaluates your knowledge of BST properties and efficient tree traversal algorithms.
Why Interviewers Ask This
It tests your ability to leverage specific tree properties (BST ordering) to solve problems faster than general tree approaches. Interviewers want to see if you can write concise, optimal code that exploits the sorted nature of BSTs. It also checks your understanding of recursion and path finding.
How to Answer This Question
Explain that since it is a BST, you can compare node values with the target nodes to decide direction. Start from the root and move left if both targets are smaller, or right if both are larger. The first node where targets split is the LCA. Mention handling null cases and single-node trees briefly.
Key Points to Cover
- Exploit BST property
- Compare values with root
- Single pass traversal
- O(h) time complexity
Sample Answer
In a BST, the LCA is the deepest node that lies between the two given nodes. Starting from the root, if both target values are less than the current node, I move left. If both are greater, I move right. The first node wh…
Common Mistakes to Avoid
- Treating it as a generic binary tree
- Not handling edge cases
- Confusing parent-child relationships
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