BFS on matrix
Last updated: August 2, 2025
Quick Overview
Implement a Breadth-First Search (BFS) algorithm to traverse a given 2D matrix, where each cell can either be a passable space (represented by 0) or an obstacle (represented by 1). Your function should return the shortest path length from the top-left corner to the bottom-right corner of the matrix, or -1 if there is no valid path.
OpenAI
August 2, 20250
3
4,283 solved
Implement a Breadth-First Search (BFS) algorithm to traverse a given 2D matrix, where each cell can either be a passable space (represented by 0) or an obstacle (represented by 1). Your function should return the shortest path length from the top-left corner to the bottom-right corner of the matrix, or -1 if there is no valid path.
This coding problem is frequently asked during Phone Screen at OpenAI. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. OpenAI expects candidates to write production-quality code, not just solve the puzzle.
What the Interviewer Expects
- Identify the correct data structure and algorithm for the problem
- Write clean, bug-free code with proper variable naming
- Analyze time and space complexity correctly
- Handle basic edge cases (empty input, single element)
- Communicate your thought process while coding
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)?
- How would your solution change if the input was sorted?
- What happens if the input contains duplicates?
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Problem Analysis
This problem requires us to find the shortest path in a grid (2D matrix) from the top-left corner to the bottom-right corner. The BFS (Breadth-First Search) algorithm is appropriate here because it ex...
Approach
- Initialization: Start by checking if the start (0,0) or end (n-1,m-1) positions are blocked (value 1). If so, return -1 immediately.
- Queue Setup: Create a queue to facilitate the BFS and...
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