Count kth largest element in matrix
Last updated: September 3, 2025
Quick Overview
Given a 2D matrix of integers, write a function to find the kth largest element in the matrix. The matrix is not necessarily sorted, and you should return the kth largest element as an integer. The input will consist of the matrix and an integer k, and you should ensure that k is valid within the bounds of the matrix size.
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Given a 2D matrix of integers, write a function to find the kth largest element in the matrix. The matrix is not necessarily sorted, and you should return the kth largest element as an integer. The input will consist of the matrix and an integer k, and you should ensure that k is valid within the bounds of the matrix size.
Google uses this problem in the Phone 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
- Identify the correct data structure and algorithm for the problem
- Write clean, bug-free code with proper variable naming
- Analyze time and space complexity correctly
- Handle basic edge cases (empty input, single element)
- Communicate your thought process while coding
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 your solution change if the input was sorted?
- What happens if the input contains duplicates?
- What is the worst-case input for your solution?
- How would you modify your solution to handle streaming input?
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Problem Analysis
To solve the problem of finding the kth largest element in a 2D matrix, we can utilize the min-heap data structure. The reason a min-heap is ideal here is that it allows us to efficiently keep tra...
Approach
- Flatten the Matrix: Convert the 2D matrix into a 1D list of elements. For example, given the matrix [[3, 2, 1], [5, 6, 4]], the flattened list would be [3, 2, 1, 5, 6, 4].
- Use a Min-Heap...
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