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Meta·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
May 2026

Summary

Meta SWE interview with a grid manipulation problem. Pretty focused on getting the implementation right under pressure.

Questions Asked (1)

Q1

Given a 2D maze grid with a marked entry ('e') and exit ('E'), and a list of coordinate pairs representing a path through the maze, mark every point along the path with '*' except the entry and exit, then print the resulting grid.

Algorithms & Data Structures
Author's notes

Seemed straightforward at first glance.

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AI HintsAI Generated

Suggested Approach

First, clarify the problem constraints and edge cases, such as whether the path includes the entry and exit, and if the path is guaranteed valid. Then, iterate through the path coordinates, updating the grid with '*' for each point except the entry and exit. Finally, print the grid row by row.

Pro tip: Demonstrate attention to detail by handling edge cases like empty path, path with only entry and exit, and ensuring you don't overwrite 'e' or 'E'. Also, discuss time and space complexity to show efficiency awareness.

1. Clarify requirements and edge cases

Ask clarifying questions: Does the path include the entry and exit? Can the path revisit cells? Is the path guaranteed to be valid? How should the grid be printed (e.g., as strings)?

2. Choose data structures and algorithm

Decide to use a 2D list (or array) for the grid and a set for path coordinates for O(1) lookups if needed. The algorithm will iterate through the path and update the grid.

3. Implement the marking logic

Loop over each coordinate in the path. If the cell is not 'e' or 'E', set it to '*'. Be careful to preserve the entry and exit markers.

4. Print the resulting grid

Iterate through each row of the grid and print it as a string, ensuring proper formatting (e.g., no extra spaces).

5. Analyze complexity and test

State time complexity O(P) where P is path length, and space complexity O(1) extra if modifying in place. Walk through a small example to verify correctness.

Key Points to Mention

  • Edge cases: empty path, path with only entry and exit, path containing invalid coordinates
  • Preserving entry and exit markers while marking other cells
  • Time and space complexity analysis
  • Choice of data structures (2D array, set for path if needed)
  • Modular code with clear separation of concerns (e.g., function to mark path, function to print grid)
  • Testing with a simple example to demonstrate correctness

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.