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Implement BFS and a Job Scheduler | Nuro Interview Question

Q: Implement BFS and a Job Scheduler

This question evaluates algorithmic problem-solving and concurrency engineering skills by combining a BFS-based grid-reveal algorithm for minefield traversal and a thread-safe periodic job scheduler requiring synchronization and scheduling semantics.

The interview report described two coding questions in the same category:

Grid reveal with BFS You are given an m x n board representing a hidden minefield. Each cell is one of:
- M : unrevealed mine
- E : unrevealed empty cell
- B : revealed blank cell with no adjacent mines
- 1 - 8 : revealed cell showing the number of adjacent mines
- X : revealed mine after a click
Given a click position (row, col) , update the board using these rules:
- If the clicked cell is a mine ( M ), change it to X .
- Otherwise, reveal cells using BFS :
  - Count the number of mines in the 8 neighboring cells.
  - If the count is greater than 0, write that digit in the cell and stop expanding from it.
  - If the count is 0, mark the cell as B and continue revealing its unrevealed neighbors.
Return the updated board.
Concurrent periodic job scheduler Implement a thread-safe in-memory scheduler that supports periodic jobs. Each job has:
- a unique jobId
- an execution interval such as every N milliseconds
- a callback function to run
Support the following operations:
- register(jobId, intervalMs, task)
- cancel(jobId)
- start()
- stop()
Requirements:
- Multiple worker threads may execute jobs concurrently.
- A job should be triggered approximately once per interval.
- The same scheduled run must not execute more than once.
- Cancellation must be safe even if other threads are polling or executing jobs.
- Explain how you would handle cases where a task runs longer than its interval, clock drift, and backpressure under heavy load.

The interview report described two coding questions in the same category:

Grid reveal with BFS You are given an m x n board representing a hidden minefield. Each cell is one of:
- M : unrevealed mine
- E : unrevealed empty cell
- B : revealed blank cell with no adjacent mines
- 1 - 8 : revealed cell showing the number of adjacent mines
- X : revealed mine after a click
Given a click position (row, col) , update the board using these rules:
- If the clicked cell is a mine ( M ), change it to X .
- Otherwise, reveal cells using BFS :
  - Count the number of mines in the 8 neighboring cells.
  - If the count is greater than 0, write that digit in the cell and stop expanding from it.
  - If the count is 0, mark the cell as B and continue revealing its unrevealed neighbors.
Return the updated board.
Concurrent periodic job scheduler Implement a thread-safe in-memory scheduler that supports periodic jobs. Each job has:
- a unique jobId
- an execution interval such as every N milliseconds
- a callback function to run
Support the following operations:
- register(jobId, intervalMs, task)
- cancel(jobId)
- start()
- stop()
Requirements:
- Multiple worker threads may execute jobs concurrently.
- A job should be triggered approximately once per interval.
- The same scheduled run must not execute more than once.
- Cancellation must be safe even if other threads are polling or executing jobs.
- Explain how you would handle cases where a task runs longer than its interval, clock drift, and backpressure under heavy load.

Implement BFS and a Job Scheduler

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Implement BFS and a Job Scheduler

Quick Overview

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