Count connected components in matrix
Last updated: September 5, 2025
Quick Overview
Given a 2D matrix consisting of 0s and 1s, where 1s represent land and 0s represent water, write a function to count the number of connected components of land. Two land cells are considered connected if they are adjacent horizontally or vertically. The function should return an integer representing the total number of connected components in the matrix.
Rippling
September 5, 202529
8
1,757 solved
Given a 2D matrix consisting of 0s and 1s, where 1s represent land and 0s represent water, write a function to count the number of connected components of land. Two land cells are considered connected if they are adjacent horizontally or vertically. The function should return an integer representing the total number of connected components in the matrix.
Rippling uses this problem in the Take-home Project 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
- Can you solve this iteratively instead of recursively (or vice versa)?
- Can you optimize the space complexity of your solution?
- What happens if the input contains duplicates?
- Can you solve this in a single pass?
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Practice DSA ProblemsSample Answer
Problem Analysis
In this problem, we need to count the number of connected components of land ('1's) in a 2D matrix. The connection is defined as being adjacent either horizontally or vertically. This situation can be...
Approach
- Initialize a variable
countto zero to keep track of the number of connected components. - Loop through each cell in the matrix. For each cell:
- If the cell's value is '1', it means we found...
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