Grid BFS: find shortest path with obstacles using breadth-first search

Grid BFS: In a rectangular 0/1 grid, find the minimum number of four-direction moves from the top-left cell to the bottom-right cell. Cells with 1 are blocked; return -1 when unreachable.

Input: A JSON object { "grid": number[][] } containing only 0 and 1.

Output: A JSON integer move count, or -1.

Constraints:

0 <= rows, columns <= 500
The grid is rectangular
Movement is allowed up, down, left, and right only

Read one JSON value from stdin and print exactly one JSON-serialized answer to stdout with no extra text.

Difficulty: EASY. Variant: 1. Expect follow-up questions about complexity, edge cases, and alternative approaches.

Practice context

This coding (algo) exercise trains prompt interpretation, explicit assumptions, a concrete response, and a concise explanation of the decisions made. It is marked easy difficulty.

The signed-in workspace provides the tools required

What this task practices

This coding (algo) exercise trains the same sequence expected in an interview: understand the prompt, make assumptions explicit, produce a concrete answer, and explain the decisions behind it. The task is marked easy difficulty. The private workspace adds the tools required by this round, such as recording, code execution, diagrams, evidence panels, or structured notes. It also preserves the attempt so later feedback can be compared with previous work. Evaluation is based on task-specific criteria and the candidate seniority selected in the preparation path. Public pages never expose the reference solution, hidden tests, evaluator instructions, or another candidate’s work.