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Rotting Oranges

In a grid, 0 is empty, 1 is a fresh orange, and 2 is rotten. Every minute, a rotten orange rots any fresh orange directly adjacent (up/down/left/right). Return the number of minutes until no fresh orange remains, or -1 if some can never rot.

Figure

row · column

Examples

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

out: 4

all rot after 4 minutes

Constraints

1 <= rows, cols <= 100
grid[i][j] is 0, 1, or 2

Hints

target: O(rows*cols) time⌘↩ run · ⇧⌘↩ submit