Created
April 6, 2020 02:40
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Oranges Rotting
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| from collections import deque | |
| class Solution(object): | |
| def orangesRotting(self, grid): | |
| """ | |
| :type grid: List[List[int]] | |
| :rtype: int | |
| """ | |
| # corner cases | |
| if not grid or not grid[0]: | |
| return 0 | |
| n = len(grid) | |
| m = len(grid[0]) | |
| queue = deque() | |
| visited = set() | |
| # init multiple starting vertices | |
| for i in range(n): | |
| for j in range(m): | |
| if grid[i][j] == 2: | |
| # start with depth = 0 | |
| queue.appendleft((i, j, 0)) | |
| visited.add((i, j)) | |
| # BFS | |
| d = 0 | |
| while queue: | |
| r, c, d = queue.pop() | |
| for i, j in [[r + 1, c], [r, c + 1], [r - 1, c], [r, c - 1]]: | |
| # valid neighbours | |
| if 0 <= i < n and 0 <= j < m: | |
| if grid[i][j] == 1 and (i, j) not in visited: | |
| queue.appendleft((i, j, d + 1)) | |
| visited.add((i, j)) | |
| # check if there are still fresh oranges | |
| for i in range(n): | |
| for j in range(m): | |
| if grid[i][j] == 1 and (i, j) not in visited: | |
| return -1 | |
| return d |
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