Find connected components in grid
Last updated: July 1, 2025
Quick Overview
Given a 2D grid of 0s and 1s, where 1s represent land and 0s represent water, write a function to find all connected components of land in the grid. A connected component is defined as a group of adjacent 1s connected horizontally or vertically. The function should return a list of lists, where each inner list contains the coordinates of the cells that make up a connected component.
Twilio
July 1, 202510
11
2,988 solved
Given a 2D grid of 0s and 1s, where 1s represent land and 0s represent water, write a function to find all connected components of land in the grid. A connected component is defined as a group of adjacent 1s connected horizontally or vertically. The function should return a list of lists, where each inner list contains the coordinates of the cells that make up a connected component.
This coding problem is frequently asked during Technical Screen at Twilio. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Twilio expects candidates to write production-quality code, not just solve the puzzle.
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 optimize the space complexity of your solution?
- How would your solution change if the input was sorted?
- Can you solve this iteratively instead of recursively (or vice versa)?
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Practice DSA ProblemsSample Answer
Problem Analysis
To solve the problem of finding connected components in a 2D grid, we can identify that the best pattern to use here is Depth-First Search (DFS). This is because we need to explore each connected comp...
Approach
- Initialize an empty list to hold the connected components. 2. Create a visited matrix of the same size as the grid to keep track of which cells have already been processed. 3. Iterate through each ...
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