Count Rectangle Coverage on a Grid
Last updated: July 21, 2026
Quick Overview
The candidate is asked to write a function that counts the number of rectangles that can be formed on a given grid based on specified coordinates.
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The candidate is asked to write a function that counts the number of rectangles that can be formed on a given grid based on specified coordinates.
This question is typically asked during the onsite coding round to evaluate a candidate's problem-solving skills and ability to work with algorithms. The interviewer is looking for a clear understanding of grid-based problems and how to efficiently count combinations of points to form rectangles. The candidate's approach to coding, optimization, and edge cases will also be assessed.
What the Interviewer Expects
- Clearly explain the approach before coding.
- Identify the coordinates that define the rectangles.
- Implement a solution that efficiently counts rectangles.
- Discuss time and space complexity of the solution.
- Handle edge cases and provide test cases.
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 optimize your solution for larger grids?
- Can you explain how you would handle overlapping rectangles?
- What would you change if the grid size was dynamic?
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Practice DSA ProblemsSample Answer
Approach
To count the number of rectangles that can be formed on a grid, we need to identify pairs of coordinates. Each rectangle can be defined by two opposite corners (top-left and bottom-right). Therefore, ...
Algorithm
- Create a set to store unique points from the grid.
- Iterate through all pairs of points in the set.
- For each pair, check if the other two corners of the rectangle exist in the set.
- If th...
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