Coding

Custom Tree Sum

Asked atJTJosh Technology Group

1Give yourself 5 minutes

2Answer out loud, not in your head

3Then compare with the answer below

Stuck? Show a way to structure it+

01Ask what custom means and what values participate.
02Define the return value for one subtree.
03Use postorder so child aggregates exist first.
04Combine child results with the node value or rule.
05Specify overflow and empty-tree behavior.

Reference answer

The phrase “custom tree sum” does not define which nodes or operation count, so ask for the exact rule, an example, tree shape, and whether values may be negative. Once confirmed, use a postorder DFS invariant: helper(node) returns the aggregate required for node's subtree. The base case for null is the identity element, usually zero for addition. Compute child aggregates first, apply the stated custom rule at the node, and return the result upward; a global accumulator is appropriate only when the desired value is not the same as the returned subtree aggregate. State whether a wide numeric type is needed. Do not assume a binary tree or ordinary sum from the title. A full traversal is O(n) time and O(height) recursion space.

Then expect these follow-ups

What is the exact custom rule and a sample tree?
Tests: follow-up reasoning
Should the result include all nodes or only leaves?
Tests: follow-up reasoning

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