Most Frequent Subtree Sum

MediumTreesdfs

Solve this the way you would in the interview: out loud, on a timer, with an AI interviewer asking follow-ups while you code. You get a scored report at the end.

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Problem

The **subtree sum** of a node is the sum of the values of every node in the subtree rooted there, the node itself included. Given the root of a non-empty binary tree, compute the subtree sum of every node and return the sum(s) that occur most often. If several sums tie for the highest frequency, return all of them. Return the result sorted in **ascending** order.

Examples

Input: root = [5,2,-3]
Output: [-3,2,4]
The subtree sums are 2, -3 and 4, each appearing once.
Input: root = [5,2,-5]
Output: [2]
The sums are 2, -5 and 2, so 2 is the most frequent.

Constraints

  • 1 <= number of nodes <= 10^4
  • -10^5 <= Node.val <= 10^5

What the interviewer grades

A correct solution is one of five scores. The report also grades problem understanding (did you clarify inputs and edge cases before coding), problem solving, communication while you work, code quality, and testing. See a sample report, or read up on the pattern in the lessons.

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