What is the Rotting Oranges pattern?

The Rotting Oranges is a common coding interview pattern in Breadth First Search problems. It provides a structured approach to solving related algorithm challenges efficiently.

When should I use Rotting Oranges?

Use the Rotting Oranges pattern when you encounter problems matching its characteristics. Check the "When to Use" and "Clues" sections in the lesson for specific indicators.

Is Rotting Oranges asked in FAANG interviews?

Yes, Rotting Oranges is an essential pattern commonly tested in FAANG and top tech company technical interviews.

Breadth-First Search

Medium

Rotting Oranges

Determine the minimum time required to rot all oranges.

20 min

Solve on LeetCode

Problem Understanding

You have a grid with:

0: Empty cell
1: Fresh orange
2: Rotten orange

Every minute, a rotten orange infects its 4-directionally adjacent fresh neighbors. Return minimum minutes until no fresh orange remains. If impossible, return -1.

Algorithm Strategy

This simulates a process expanding over time, which is classic BFS.

Multi-source: Start with ALL initially rotten oranges in the Queue.
Count Fresh: Count total fresh oranges initially. If 0, return 0.
Level-by-Level: Process the queue layer by layer (minutes). Each layer spreads rot to neighbors.
- Decrement fresh_count whenever a fresh orange rots.
Completion: If queue empty and fresh_count == 0, return time. Else return -1.

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