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Meta·Software Engineer·Onsite - Coding / Algorithms·Senior

SeniorPrefer not to say
May 2026

Summary

Meta SWE coding round with a BFS maze problem that had a twist: one-way chutes that force your movement direction. Not the hardest problem on paper, but the forced-move mechanic tripped me up more than I expected.

Questions Asked (1)

Q1

Given an R x C maze grid with walls, open cells, a start, an end, and one-way chutes that can only be entered from the left and force you one step to the right, find the minimum number of steps from start to end using BFS, or return -1 if unreachable.

Algorithms & Data Structures
Author's notes

My first instinct was standard BFS and I started coding before fully thinking through the chute mechanic.

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AI HintsAI Generated

Suggested Approach

Model the maze as a graph where each cell is a node, and edges represent valid moves (up, down, left, right, and forced right via chutes). Use BFS to find the shortest path from start to end, ensuring that chute moves are handled correctly (only enter from left, then forced right). If BFS exhausts without reaching the end, return -1.

Pro tip: Clarify the chute behavior upfront: confirm that entering a chute from the left immediately moves you one step right, and that you cannot enter from other directions. This shows attention to detail and avoids incorrect assumptions.

1. Understand the problem and clarify rules

Restate the problem to ensure you understand the grid, movement rules, and chute behavior. Ask clarifying questions if needed, especially about chute entry and exit conditions.

2. Define the state and transitions

Represent each cell as a state. Define valid moves: up, down, left, right (if not blocked), and special chute moves (if the current cell is a chute and you enter from the left, you move right).

3. Implement BFS

Use a queue to perform BFS from the start cell, tracking visited cells to avoid cycles. For each cell, enqueue all valid neighboring cells (including chute-forced moves) and increment the step count.

4. Handle termination and return result

If the end cell is reached, return the number of steps. If the queue empties without reaching the end, return -1.

5. Analyze complexity and edge cases

Discuss time and space complexity (O(R*C) for both). Mention edge cases: start equals end, no path, chutes at boundaries, and multiple chutes.

Key Points to Mention

  • BFS guarantees shortest path in unweighted graphs.
  • Chute moves are deterministic and forced, so they can be treated as additional edges in the graph.
  • Visited set prevents infinite loops and ensures O(R*C) time.
  • Edge cases: start == end, unreachable end, chutes that lead out of bounds or into walls.
  • Space complexity can be optimized by using a 2D array for visited instead of a set.
  • Clarify if chutes can be entered from other directions or if they are one-way only from left.

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