994 - Rotting Oranges.

Medium

You are given an m x n grid where each cell can have one of three values:

• 0 representing an empty cell,

• 1 representing a fresh orange, or

• 2 representing a rotten orange.

Every minute, any fresh orange that is 4-directionally adjacent to a rotten orange becomes rotten.

Return the minimum number of minutes that must elapse until no cell has a fresh orange. If this is impossible, return -1.

Example 1:

Input: grid = [2,1,1,1,1,0,0,1,1]

Output: 4

Example 2:

Input: grid = [2,1,1,0,1,1,1,0,1]

Output: -1

Explanation: The orange in the bottom left corner (row 2, column 0) is never rotten, because rotting only happens 4-directionally.

Example 3:

Input: grid = [0,2]

Output: 0

Explanation: Since there are already no fresh oranges at minute 0, the answer is just 0.

Constraints:

• m == grid.length

• n == grid[i].length

• 1 <= m, n <= 10

• grid[i][j] is 0, 1, or 2.