Walls and Gates

You are given an m x n grid rooms filled with three possible values:

• -1 - a wall or obstacle
• 0 - a gate
• 2147483647 - INF (= 2^31 - 1), representing an empty room

Fill each empty room with the distance to its nearest gate. If it is impossible to reach a gate, leave it as 2147483647. Modify rooms in-place; the function returns None.

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Example 1

INF = 2147483647

rooms = [
  [INF, -1,   0, INF],
  [INF, INF, INF,  -1],
  [INF,  -1, INF,  -1],
  [  0,  -1, INF, INF]
]

Input: rooms above
Output: [[3, -1, 0, 1], [2, 2, 1, -1], [1, -1, 2, -1], [0, -1, 3, 4]]
Explanation: Each empty room is filled with the shortest distance to the nearest gate.
             Rooms that cannot reach any gate remain INF (2147483647 in output).

Example 2

rooms = [[INF, -1, INF], [-1, 0, -1], [INF, -1, INF]]

Input: rooms above
Output: [[2147483647, -1, 2147483647], [-1, 0, -1], [2147483647, -1, 2147483647]]
Explanation: The gate at the center is completely surrounded by walls,
             so none of the corner rooms can be reached.

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Constraints

• m == rooms.length
• n == rooms[i].length
• 1 <= m, n <= 250
• rooms[i][j] is one of -1, 0, or 2147483647