Count connected components in grid
Last updated: October 3, 2025
Quick Overview
Given a 2D grid 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 take the grid as input and return the total count of connected components.
Morgan Stanley
October 3, 202538
3
3,374 solved
Given a 2D grid 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 take the grid as input and return the total count of connected components.
This coding problem is frequently asked during Take-home Project at Morgan Stanley. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Morgan Stanley 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 solve this iteratively instead of recursively (or vice versa)?
- Can you solve this in a single pass?
- How would you parallelize this solution?
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Practice DSA ProblemsSample Answer
Problem Analysis
This problem can be analyzed using the Depth First Search (DFS) or Breadth First Search (BFS) algorithm patterns. The reason why DFS or BFS applies here is that we need to explore all connected '1's (...
Approach
- Initialize a counter to track the number of connected components.
- Iterate through each cell in the grid. For each '1' (land) found, increment the counter and initiate a DFS/BFS from that cell. 3...
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