Find connected components in matrix
Last updated: May 27, 2026
Quick Overview
Given a binary matrix, write a function to find all connected components of 1s (representing land) and return a list of these components, where each component is represented by a list of its coordinates. The function should efficiently traverse the matrix using Depth-First Search (DFS) or Breadth-First Search (BFS) to identify and group connected 1s, and the output should be a list of lists, with each inner list containing the coordinates of a connected component.
Bloomberg
May 27, 202621
7
3,976 solved
Given a binary matrix, write a function to find all connected components of 1s (representing land) and return a list of these components, where each component is represented by a list of its coordinates. The function should efficiently traverse the matrix using Depth-First Search (DFS) or Breadth-First Search (BFS) to identify and group connected 1s, and the output should be a list of lists, with each inner list containing the coordinates of a connected component.
Bloomberg uses this problem in the Phone Screen 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
- Quickly identify the optimal approach and its theoretical basis
- Handle complex algorithm design with multiple interacting components
- Write concise, elegant code under time pressure
- Prove correctness of your approach and discuss alternative solutions
- Optimize beyond the obvious: discuss constant factor improvements
- Address follow-up variations and explain how the solution generalizes
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?
- Can you solve this in a single pass?
- What happens if the input contains duplicates?
- Can you solve this iteratively instead of recursively (or vice versa)?
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Practice DSA ProblemsSample Answer
Problem Analysis
In this problem, we are tasked with finding all connected components of 1s in a binary matrix, where connected components are defined as groups of adjacent 1s in the four cardinal directions (up, down...
Approach
- Initialize a visited matrix: Create a 2D list to keep track of which cells have already been visited.
- Iterate through the matrix: For each cell in the matrix, if the cell is 1 and has no...
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