How do you find the size of the largest BST subtree inside a binary tree?
PICTURE THIS: HOW TO EXPLAIN IT
Simple meaning
Postorder return (is_bst, min, max, size) for each subtree.
WHY — BST instead of guessing?
Why interviewers care about BST:
question about BST.
trade-offs, and what you would actually do on a DSA project - not buzzwords.
Name the idea, why it exists, then one short example.
End with when you use it and one common pitfall.
STEPS — What happens step by step?
Before you speak the answer, walk the interviewer through these steps:
- 1Postorder return (is_bst, min,
max, size) for each subtree.
- 2A node is a
BST if both children are BSTs and node value sits between left.max and right.min
- 3then size is 1+left+right,
else take the max child size.
- 4Time is O(n) and
space is O(h).
- 5Checking isValidBST at every
node is O(n^2).
- 6Close
When you pick this over the alternative.
EXAMPLE — See it in action
Here's a short line you can speak, broken into clear beats:
Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.
Key takeaway
Postorder return (is_bst, min, max, size) for each subtree. A node is a BST if both children are BSTs and node value sits between left.max and right.min