1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
| class Solution:
def maximumSafenessFactor(self, grid: List[List[int]]) -> int:
A = [] # thieves
m, n = len(grid), len(grid[0])
for i in range(m):
for j in range(n):
if grid[i][j] == 1:
A.append([i, j])
visited = [[0 for j in range(n)] for i in range(m)]
distance = [[0 for j in range(n)] for i in range(m)]
# find the minimum mahatten distance of each cell to theives
depth = 0
while A:
B = []
for i, j in A:
if not visited[i][j]:
visited[i][j] = 1
distance[i][j] = depth
for x, y in [[i + 1, j], [i - 1, j], [i, j + 1], [i, j - 1]]:
if 0 <= x < m and 0 <= y < n:
B.append([x, y])
A = B
depth += 1
# start from 0,0 and use dijkstra
visited = [[0 for j in range(n)] for i in range(m)]
pq = [[-distance[0][0], 0, 0]]
while pq:
dis, i, j = heapq.heappop(pq)
if visited[i][j]:
continue
visited[i][j] = 1
if i == m - 1 and j == n - 1:
return -dis
for x, y in [[i + 1, j], [i - 1, j], [i, j + 1], [i, j - 1]]:
if 0 <= x < m and 0 <= y < n:
heapq.heappush(pq, [-min(-dis, distance[x][y]), x, y])
return -1
|