Solve frequency and tree-completeness problems
Company: Meta
Role: Machine Learning Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Onsite
## Problem A: Return the *k* most frequent values
You are given an integer array `nums` and an integer `k`.
**Task:** Return the `k` distinct values that occur most frequently in `nums`.
**Input**
- `nums`: list of integers (length `n`)
- `k`: integer, `1 <= k <= (# of distinct values in nums)`
**Output**
- A list of `k` integers: the values with highest frequency.
**Notes / Constraints**
- If multiple answers are possible due to ties, any valid order is acceptable.
- Aim for better than `O(n log n)` if possible.
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## Problem B: Check whether a binary tree is complete
You are given the `root` of a binary tree.
A binary tree is **complete** if:
1. Every level except possibly the last is completely filled, and
2. All nodes in the last level are as far left as possible.
**Task:** Return `true` if the tree is complete; otherwise return `false`.
**Input**
- `root`: root node of a binary tree (each node has `val`, `left`, `right`)
**Output**
- Boolean: whether the tree is complete.
**Constraints**
- Up to ~`10^5` nodes.
Quick Answer: These two problems evaluate competency in frequency counting and selection algorithms for identifying top-k elements and in binary tree structure analysis and traversal for checking completeness, belonging to the Coding & Algorithms domain and the broader data structures and algorithms category.