Count kth largest element in matrix
Last updated: March 2, 2026
Quick Overview
Given a 2D matrix of integers, write a function to find the kth largest element in the matrix. The function should take the matrix and an integer k as inputs and return the kth largest element as output. The matrix is guaranteed to have at least k elements.
Confluent
March 2, 202624
5
3,808 solved
Given a 2D matrix of integers, write a function to find the kth largest element in the matrix. The function should take the matrix and an integer k as inputs and return the kth largest element as output. The matrix is guaranteed to have at least k elements.
Confluent uses this problem in the Technical Screen to evaluate your algorithmic thinking. They expect you to discuss multiple approaches, analyze trade-offs between them, and implement the optimal solution with clean, readable code.
What the Interviewer Expects
- Recognize the underlying problem pattern (sliding window, two pointers, BFS/DFS, etc.)
- Discuss multiple approaches and trade-offs before coding
- Implement an optimal solution with clean, production-quality code
- Handle all edge cases including boundary conditions and invalid input
- Optimize both time and space complexity with clear justification
- Test your solution systematically with well-chosen examples
Key Topics to Cover
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 happens if the input contains duplicates?
- How would you modify your solution to handle streaming input?
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Practice DSA ProblemsSample Answer
Problem Analysis
To solve the problem of finding the kth largest element in a 2D matrix, we can recognize that the matrix can be treated as a single sorted list if we consider the values across rows and columns. The k...
Approach
- Create a Min Heap: Initialize a min heap to store the top k largest elements.
- Iterate Through the Matrix: Loop through each element in the matrix:
- If the size of the heap is less th...
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