How do you find the lowest common ancestor in a binary search tree?
This question focuses on leveraging the unique properties of BSTs to find the LCA efficiently. It tests logical reasoning and tree navigation skills.
Why Interviewers Ask This
Finding the LCA in a BST is more efficient than in a general binary tree due to ordering properties. Interviewers want to see if candidates recognize these properties to achieve O(H) time complexity instead of O(N).
How to Answer This Question
Explain that in a BST, if both nodes are smaller than the root, the LCA is in the left subtree. If both are larger, it is in the right. If they split, the current root is the LCA. Describe the iterative approach for better space efficiency.
Key Points to Cover
- Leverage BST ordering property
- Compare node values with root
- Iterative solution preferred
- Time complexity O(h)
Sample Answer
In a BST, I compare the values of the two nodes with the root. If both are less than the root, I move to the left child. If both are greater, I move to the right. If the values split around the root, then the root is the lowest common ancestor. This allows me to solve it in O(h) time without extra space.
Common Mistakes to Avoid
- Treating it like a general binary tree
- Not handling equal values correctly
- Using unnecessary recursion depth
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