Problem 30: Find Distance to nearest Exit[Google]

Shortest Distance, Graph Traversal, Path Finding

What’s shaking my awesome readers,

Today’s question is a favorite of Google. It tests your knowledge, problem-solving ability, and ability to recognize the right approach. Let’s get into it.

Problem

This problem was asked by Google.

You are given a m x n 2D grid initialized with these three possible values:

-1 - A wall or an obstacle.
0 - A gate.
INF - Infinity means an empty room.

Fill each empty room with the distance to its nearest gate. If it is impossible to reach a gate, it should be filled with INF.

For example, given the 2D grid:
INF -1 0 INF
INF INF INF -1
INF -1 INF -1
0 -1 INF INF

After running your function, the 2D grid should be:
3 -1 0 1
2 2 1 -1
1 -1 2 -1
0 -1 3 4

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