Lowest Common Ancestor of a Binary Tree
A medium-tier problem at 67% community acceptance, tagged with Tree, Depth-First Search, Binary Tree. Reported in interviews at Wix and 18 others.
Lowest Common Ancestor of a Binary Tree is a medium-difficulty tree problem that appears in interviews at Meta, Amazon, LinkedIn, and Oracle. It's deceptively simple to misread: you're not searching for values, you're finding the actual node that's the deepest ancestor of two given nodes. The 66% acceptance rate masks a real trick that catches unprepared candidates mid-assessment. If you blank on the recursion pattern during the live OA, StealthCoder surfaces a working solution in seconds, invisible to the proctor.
Companies that ask "Lowest Common Ancestor of a Binary Tree"
Lowest Common Ancestor of a Binary Tree is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Built by a senior engineer who knows the OA is theater. This is the script.
Get StealthCoderThe trap is thinking bottom-up when you need to think recursion-first. Most candidates start coding a path-finding approach or try to track parent pointers. The actual solution is clean: recurse down both subtrees, and the first node where both p and q are found (or one of them is the node itself) is your LCA. The depth-first search isn't obvious until you see it. Common failure modes are forgetting null checks, mixing up what you're returning at each level, or trying to validate before you've fully traversed. This is exactly where a quick glance at a correct implementation during your assessment saves 10+ minutes of debugging. StealthCoder handles the recursion structure so you can move on.
Pattern tags
You know the problem.
Make sure you actually pass it.
Lowest Common Ancestor of a Binary Tree recycles across companies for a reason. It's medium-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Built by a senior engineer who knows the OA is theater. This is the script. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Lowest Common Ancestor of a Binary Tree interview FAQ
Is this problem still asked at top companies?+
Yes. It appears across Meta, Amazon, LinkedIn, Oracle, and at least 14 other companies in recent reports. It's a classic that doesn't go out of style because it tests both tree traversal and recursion understanding in one clean package.
What's the main trick everyone misses?+
Candidates often over-engineer it by finding paths to p and q separately, then comparing. The trick is that LCA emerges naturally from DFS: return the node where both subtree searches succeed. If you see the recursion structure first, the code writes itself.
How does this relate to the Depth-First Search topic?+
The entire solution IS DFS. You traverse the tree recursively, and at each node you check if p or q lives in the left subtree, right subtree, or is the current node. The search pattern is the algorithm. That's why the topic tag is there.
Can I solve this iteratively?+
Yes, but it's messier. You'd track parents and use a stack or queue. The recursive version is what gets asked and what interviewers expect to see. It's also what you'll code faster under time pressure.
What edge cases sink people?+
One of p or q being an ancestor of the other (it's still the LCA). Both p and q being the same node. Nodes not in the tree at all (though problems vary on this). The recursive approach handles the first two naturally if you're careful about your base cases.
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