Rotting Oranges

Redundant Connection

Course Schedule

Find how many minutes are needed for rot to spread to every fresh orange.

A grid uses `0` for empty, `1` for a fresh orange, and `2` for a rotten orange. Each minute, rot spreads horizontally and vertically. Return the minimum minutes until no fresh orange remains, or `-1` if impossible.

## Example
```
Input: {"grid":[[2,1,1],[1,1,0],[0,1,1]]}
Output: 4
```

**Constraints**
- 1 <= grid.length, grid[i].length <= 10
- Every cell is 0, 1, or 2.

**Follow-up**
Why does multi-source BFS produce the minimum time?

- Identify the required output and the state that changes.
- Use the examples to rule out tempting but incorrect interpretations.

Understand the Goal

- This problem is best exposed by Multi-source BFS expands one minute-layer at a time.
- Maintain only the state needed for the next operation.

Choose the Core Pattern

- Process each state once when possible.
- Record state before scheduling dependent work to avoid duplicates.

Build the Algorithm

- Verify the smallest input, impossible cases, and repeated values where allowed.
- Keep output ordering deterministic.