DFS on grid
Last updated: August 10, 2025
Quick Overview
Implement a Depth-First Search (DFS) algorithm to traverse a 2D grid represented by a matrix of characters. Given a starting cell, your task is to explore all connected cells of the same character and return the size of the connected component. The input will be a grid of characters, and the output should be an integer representing the size of the largest connected component found.
Redfin
August 10, 2025113
12
3,081 solved
Implement a Depth-First Search (DFS) algorithm to traverse a 2D grid represented by a matrix of characters. Given a starting cell, your task is to explore all connected cells of the same character and return the size of the connected component. The input will be a grid of characters, and the output should be an integer representing the size of the largest connected component found.
Redfin uses this problem in the Onsite 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
- 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
- How would your solution change if the input was sorted?
- What happens if the input contains duplicates?
- How would you parallelize this solution?
- Can you solve this iteratively instead of recursively (or vice versa)?
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Practice DSA ProblemsSample Answer
Problem Analysis
The problem requires using Depth-First Search (DFS) to explore a 2D grid of characters and find the size of the largest connected component of cells that share the same character. DFS is particularly ...
Approach
- Initialize a variable to keep track of the maximum size of the connected components.
- Create a visited set to track which cells have already been counted.
- Loop through each cell in the gri...
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