Coding problem: Fewest Steps Through a Warehouse. A warehouse floor is a grid given as a list of strings, one per row: `.` is open floor and `#` is a shelf. A robot starts in the top-left cell and must reach the bottom-right cell. Each step moves it one cell up, down, left or right; it can't move onto a shelf or off the grid.

What the interviewer is looking for

• What a strong solution looks like: breadth-first search from the start over open cells with a visited set (mark cells when you enqueue them); the distance when the goal is reached is the answer. O(R·C) time and space.
• Think aloud. Interviewers are judging how you reason, not only the final code.
• Be ready for: Return the path itself (parent pointers). Some cells are slower to cross — what changes (Dijkstra, 0-1 BFS)? The robot may remove one shelf: how does the state change? Many robots and the nearest exit for each (multi-source BFS).

A structure to follow: Clarify, plan, code, test, analyse

1. Step 1

   Clarify

   Restate the problem, ask about empty input, duplicates and size limits, and agree on one example.

2. Step 2

   Plan

   Say the simple approach first and its cost, then the better one. Explain why before you type.

3. Step 3

   Code

   Write small named steps and talk through each. A clear solution beats a clever one.

4. Step 4

   Test

   Walk your own example through the code, then an edge case. Fix what you find calmly.

5. Step 5

   Analyse

   State time and space cost in plain words and say what you would change for much larger input.

This is guidance on shape, not a script. Use your own real experience and facts; never invent details to fill a gap. See the STAR guide and answer frameworks.

Common slips

• Starting to code before agreeing what the answer must be.
• Going silent when stuck instead of saying what you are trying.
• Never running your own example through the code.

How to practise it

Solve it once in the editor without hints, then explain your solution aloud in under two minutes.

Related questions

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