Binary Search on matrix
Last updated: February 11, 2026
Quick Overview
Given a 2D matrix of integers where each row is sorted in ascending order and each column is also sorted in ascending order, implement a function to determine if a target value exists in the matrix. The function should return true if the target is found and false otherwise. The expected time complexity for your solution should be O(log(min(m, n))) where m is the number of rows and n is the number of columns in the matrix.
Twilio
February 11, 202611
12
2,378 solved
Given a 2D matrix of integers where each row is sorted in ascending order and each column is also sorted in ascending order, implement a function to determine if a target value exists in the matrix. The function should return true if the target is found and false otherwise. The expected time complexity for your solution should be O(log(min(m, n))) where m is the number of rows and n is the number of columns in the matrix.
Twilio 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
- 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
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
- Can you solve this iteratively instead of recursively (or vice versa)?
- How would you parallelize this solution?
- How would you test this solution thoroughly?
- Can you solve this in a single pass?
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Practice DSA ProblemsSample Answer
Problem Analysis
To solve the problem of finding a target value in a 2D matrix where each row and each column is sorted, we can leverage the properties of the matrix. The optimal approach for this problem utilizes the...
Approach
- Start at the top-right corner of the matrix. This allows us to compare the current element with the target efficiently.
- Compare the current element with the target:
- If the curren...
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