Binary Search on matrix
Last updated: July 13, 2025
Quick Overview
Given a 2D matrix of integers where each row is sorted in ascending order and the first integer of each row is greater than the last integer of the previous row, implement a function to perform a binary search to find a target value. The function should return the coordinates of the target as a tuple (row, column) if found, or (-1, -1) if the target is not present in the matrix.
PlanetScale
July 13, 202511
13
4,845 solved
Given a 2D matrix of integers where each row is sorted in ascending order and the first integer of each row is greater than the last integer of the previous row, implement a function to perform a binary search to find a target value. The function should return the coordinates of the target as a tuple (row, column) if found, or (-1, -1) if the target is not present in the matrix.
Coding interviews at PlanetScale 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
- 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
- What is the worst-case input for your solution?
- What happens if the input contains duplicates?
- Can you solve this in a single pass?
- How would you parallelize this solution?
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Practice DSA ProblemsSample Answer
Problem Analysis
This problem requires us to perform a binary search on a 2D matrix. The key characteristics of the matrix are: each row is sorted in ascending order, and the first integer of each row is greater than ...
Approach
- Matrix Dimensions: Determine the number of rows (
rows) and columns (cols) in the matrix. - Binary Search Setup: Initialize two pointers:
leftat 0 andrightatrows * cols - 1, ...
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