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Author: hogan-tech

2812-find-the-safest-path-in-a-grid/2812-find-the-safest-path-in-a-grid.py

@@ -0,0 +1,67 @@
+from collections import deque
+from typing import List
+
+
+class Solution:
+
+    dir = [(0, 1), (0, -1), (1, 0), (-1, 0)]
+
+    def maximumSafenessFactor(self, grid: List[List[int]]) -> int:
+        n = len(grid)
+        multiSourceQueue = deque()
+        for i in range(n):
+            for j in range(n):
+                if grid[i][j] == 1:
+                    multiSourceQueue.append((i, j))
+                    grid[i][j] = 0
+                else:
+                    grid[i][j] = -1
+        while multiSourceQueue:
+            size = len(multiSourceQueue)
+            while size > 0:
+                curr = multiSourceQueue.popleft()
+                for d in self.dir:
+                    di, dj = curr[0] + d[0], curr[1] + d[1]
+                    val = grid[curr[0]][curr[1]]
+                    if self.isValidCell(grid, di, dj) and grid[di][dj] == -1:
+                        grid[di][dj] = val + 1
+                        multiSourceQueue.append((di, dj))
+                size -= 1
+        start, end, res = 0, 0, -1
+        for i in range(n):
+            for j in range(n):
+                end = max(end, grid[i][j])
+        while start <= end:
+            mid = start + (end - start) // 2
+            if self.isValidSafeness(grid, mid):
+                res = mid
+                start = mid + 1
+            else:
+                end = mid - 1
+        return res
+
+    def isValidCell(self, grid, i, j) -> bool:
+        n = len(grid)
+        return 0 <= i < n and 0 <= j < n
+
+    def isValidSafeness(self, grid, minSafeness) -> bool:
+        n = len(grid)
+        if grid[0][0] < minSafeness or grid[n - 1][n - 1] < minSafeness:
+            return False
+        traversalQueue = deque([(0, 0)])
+        visited = [[False] * n for _ in range(n)]
+        visited[0][0] = True
+        while traversalQueue:
+            curr = traversalQueue.popleft()
+            if curr[0] == n - 1 and curr[1] == n - 1:
+                return True
+            for d in self.dir:
+                di, dj = curr[0] + d[0], curr[1] + d[1]
+                if self.isValidCell(grid, di, dj) and not visited[di][dj] and grid[di][dj] >= minSafeness:
+                    visited[di][dj] = True
+                    traversalQueue.append((di, dj))
+        return False
+
+
+grid = [[1, 0, 0], [0, 0, 0], [0, 0, 1]]
+print(Solution().maximumSafenessFactor(grid))