What is the algorithm to find the Lowest Common Ancestor in a BST?
This problem asks for the lowest common ancestor of two nodes in a Binary Search Tree. It leverages the unique ordering property of BSTs.
Why Interviewers Ask This
Interviewers use this to test specific knowledge of BST properties. They want to see if you can exploit the sorted nature of the tree to find the LCA in O(h) time without traversing the whole tree. It demonstrates efficient search strategies.
How to Answer This Question
Explain that in a BST, if both nodes are smaller than the current node, the LCA must be in the left subtree. If both are larger, it must be in the right subtree. If one is smaller and one is larger, or one matches the current node, then the current node is the LCA. Iterate or recurse based on these conditions. Highlight the difference between general trees and BSTs.
Key Points to Cover
- BST ordering property
- Directional movement logic
- Split point identification
- Efficient O(h) traversal
Sample Answer
In a Binary Search Tree, we can find the LCA efficiently by leveraging the ordering property. If both target nodes have values less than the current node, we move to the left child. If both are greater, we move to the ri…
Common Mistakes to Avoid
- Traversing the entire tree unnecessarily
- Confusing general tree LCA with BST LCA
- Incorrectly handling the case where one node is the ancestor
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