Count Matrix Cells Whose Row and Column Neighbors Match
Company: Hudson River Trading
Role: Software Engineer
Category: Software Engineering Fundamentals
Difficulty: medium
Interview Round: Technical Screen
Given a matrix, count how many cells have the property that every other value in the same row and every other value in the same column are all equal to each other. The candidate cell itself is excluded from this comparison.
### Constraints & Assumptions
- The matrix has at least one row and one column unless clarified.
- Exclude the candidate cell when checking its row and column.
- If there are no other compared cells, define the condition explicitly.
- Values can be compared for equality.
### Clarifying Questions to Ask
- What should happen for a 1x1 matrix?
- Does the candidate value need to equal the surrounding values?
- Are rows and columns large enough to need preprocessing?
- Can values be strings or only integers?
- Should empty matrices be allowed?
### What a Strong Answer Covers
```premium-lock What a Strong Answer Covers
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### Follow-up Questions
- How would you support updates?
- How would the answer change if the candidate cell must also match?
- Can this be solved in O(mn)?
- How would you test single-row matrices?
Quick Answer: This Hudson River Trading software engineering question asks candidates to count matrix cells whose row and column neighbors match. It is useful for practicing grid traversal, boundary checks, and translating a compact condition into maintainable code.