Leetcode 286. Walls and Gates (Multi-source BFS)

Similar patterns of multi-source BFS leetcode problems:

542. 01 Matrix
286. Walls and Gates
1765. Map of Highest Peak
1162. As Far from Land as Possible
994. Rotting Oranges

I will upload more videos about multi-source BFS leetcode problems, it's realy elegant algorithms that every cs student need to learn.

Solving multi-source BFS (Breadth-First Search) problems on LeetCode involves traversing a graph or grid starting from multiple source nodes and visiting their neighbors layer by layer. This technique is commonly used in scenarios where you need to explore multiple starting points and find the shortest path or solve related problems. Here's a general outline of the steps to solve multi-source BFS problems:

1. Understanding the Problem:
- Carefully read and understand the problem statement.
- Identify the graph or grid structure and the criteria for visiting nodes.

2. Data Structures:
- Set up data structures: queues and sets to store nodes to be visited and track visited nodes.

3. Initializing the BFS:
- Add all source nodes to the initial queue.
- Mark the source nodes as visited in visited set.

4. Breadth-First Search:
- Start a loop to process nodes in the queue.
- For each node in queue, pop out and visit its neighbors (adjacent nodes) that haven't been visited yet.
- Add the unvisited neighbors to the queue and mark them as visited.
- Continue this process layer by layer until the queue/data structure is empty.

5. Termination and Results:
- Once the BFS traversal is complete, you might have gathered the required information, solved the problem, or reached a specific destination.

6. Consider ways to further optimize your solution if necessary.

Remember that each problem on LeetCode can have unique requirements and variations. It's important to adapt the general BFS approach to the specific problem you're solving. Also, make sure to refer to the problem's specific constraints and hints provided by LeetCode to tailor your solution accordingly.