Compute Infection Time in a Grid
Company: OpenAI
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: hard
Interview Round: Technical Screen
You are given an `m x n` grid where each cell is one of the following:
- `0`: empty
- `1`: healthy
- `2`: infected
Every minute, each infected cell spreads the infection to its adjacent healthy cells in the four cardinal directions.
Return the minimum number of minutes needed until no healthy cells remain. If it is impossible to infect every healthy cell, return `-1`.
Quick Answer: This question evaluates competence in grid-based graph traversal and simulation of propagation dynamics, focusing on state management, time-step modeling, and handling unreachable cells.