How do you find the lowest common ancestor of two nodes in a binary tree (not necessarily a BST)?
PICTURE THIS: HOW TO EXPLAIN IT
IdeaTrees
HowWhat happens inside
Why they askShows real use
Simple meaning
Recurse: if the current node is p or q, return it
WHY — Trees instead of guessing?
Why interviewers care about Trees:
This is a process
question about Trees.
Panels listen for order,
trade-offs, and what you would actually do on a DSA project - not buzzwords.
Stay structured
Name the idea, why it exists, then one short example.
Close cleanly
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:
- 1Recurse: if the current
node is p or q, return it
- 2otherwise combine left and
right results.
- 3If both sides return
non-null, current is the LCA
- 4otherwise bubble up the
non-null side.
- 5Time is O(n) and
space is O(h).
- 6Parent pointers would allow
walking to root with a set in O(h).
EXAMPLE — See it in action
Here's a short line you can speak, broken into clear beats:
Say this line
“Time is O(n) and space is O(h).”
Break into beats
TimeisOnandspace
Speaking order
2987408337471632900
Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.
Key takeaway
Recurse: if the current node is p or q, return it otherwise combine left and right results.