← Snowflake Interview Insights
It's a tree averaging problem but the condition being on the root specifically threw me a bit.
Clarify the problem statement first, as it can be interpreted in two ways: either check if the root's value equals the average of all nodes in the entire tree, or check if for every subtree, the root's value equals the average of that subtree. Then, design a recursive post-order traversal that computes subtree sums and node counts, allowing you to compute averages and verify the condition efficiently in O(n) time.
Pro tip: Explicitly discuss the ambiguity in the question and propose solutions for both interpretations; this shows thoroughness and prevents you from solving the wrong problem. Also, mention that using integer division could cause precision issues, so compare using multiplication or floating-point with care.
Ask the interviewer to confirm whether the condition applies to the entire tree or to every subtree. This determines the algorithm's scope and avoids misinterpretation.
Design a post-order traversal that returns both the sum of values and the number of nodes in the subtree rooted at the current node.
At each node, compute the average of its subtree using the returned sum and count, then compare it to the node's value. If the condition is global, only check at the root; if per-subtree, check at every node.
Consider empty trees, single-node trees, and avoid floating-point inaccuracies by using cross-multiplication (value * count == sum) or a tolerance-based comparison.
State that the solution runs in O(n) time and O(h) space for the recursion stack, where n is the number of nodes and h is the tree height.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.