Merge K Sorted grids
Last updated: February 22, 2026
Quick Overview
Given k sorted binary trees, merge them into a single sorted result.
Elastic
Coding & Algorithms
Machine Learning Engineer
Elastic
February 22, 2026Machine Learning Engineer
Technical Screen
Coding & Algorithms
Hard
8
14
3,475 solved
Given k sorted binary trees, merge them into a single sorted result.
Coding interviews at Elastic focus on problem-solving approach as much as the final solution. The interviewer wants to see you break down the problem, consider edge cases, and optimize iteratively. Communication throughout the process is key.
What the Interviewer Expects
- Quickly identify the optimal approach and its theoretical basis
- Handle complex algorithm design with multiple interacting components
- Write concise, elegant code under time pressure
- Prove correctness of your approach and discuss alternative solutions
- Optimize beyond the obvious: discuss constant factor improvements
- Address follow-up variations and explain how the solution generalizes
Key Topics to Cover
Sorting and searching
Tree structures and recursion
Binary search and divide and conquer
Hash maps and frequency counting
How to Approach This
- Clarify input constraints and edge cases before writing code.
- Walk through your approach verbally and confirm with the interviewer before coding.
- Start with a brute force solution, then optimize. Mention time and space complexity.
- Test your solution with examples, including edge cases like empty input or duplicates.
- Consider common patterns: sliding window, two pointers, hash map, BFS/DFS, dynamic programming.
Possible Follow-up Questions
- How would you test this solution thoroughly?
- What is the worst-case input for your solution?
- Can you optimize the space complexity of your solution?
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Practice DSA ProblemsSample Answer
Problem Analysis
To merge k sorted binary trees into a single sorted structure, we can utilize a priority queue (min-heap). This approach is ideal because it allows us to efficiently access the smallest element ac...
Approach
- Initialize a Min-Heap: Start by creating a min-heap to store the root nodes of all k trees.
- Heapify the Roots: Insert the root of each binary tree into the min-heap. This ensures the sm...
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