In a grid, 0=empty, 1=fresh orange, 2=rotten orange. Each minute, rotten oranges spread to adjacent fresh ones. Return minutes until all rot, or -1 if impossible.
Input: [[2,1,1],[1,1,0],[0,1,1]] Output: 4 Input: [[2,1,1],[0,1,1],[1,0,1]] Output: -1
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