Topological Sort on grid
Last updated: January 14, 2026
Quick Overview
Given a grid represented as a 2D array where each cell contains a unique integer, perform a topological sort to determine a valid ordering of the cells based on their values. The output should be a list of integers representing the sorted order, ensuring that for any two cells, if one cell's value is less than another's, it appears before the latter in the output list.
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Given a grid represented as a 2D array where each cell contains a unique integer, perform a topological sort to determine a valid ordering of the cells based on their values. The output should be a list of integers representing the sorted order, ensuring that for any two cells, if one cell's value is less than another's, it appears before the latter in the output list.
This coding problem is frequently asked during Phone Screen at LinkedIn. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. LinkedIn 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
- What happens if the input contains duplicates?
- How would you test this solution thoroughly?
- How would your solution change if the input was sorted?
- How would you modify your solution to handle streaming input?
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Practice DSA ProblemsSample Answer
Problem Analysis
To solve the problem of performing a topological sort on a grid represented as a 2D array, we need to recognize that this is essentially a graph problem. Each cell in the grid can be thought of as a n...
Approach
- Create a graph representation: First, we need to create a directed graph from the grid. We'll iterate through each cell and compare its value with neighboring cells (up, down, left, right) to d...
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