Merge pull request #68 from s2gh/patch-15

Create 13. Walls and Gates.py

07_Graph/13. Walls and Gates.py

@@ -0,0 +1,24 @@
+# https://www.lintcode.com/problem/663
+
+from typing import List
+import collections
+
+class Solution:
+    def walls_and_gates(self, rooms: List[List[int]]):
+        row, col = len(rooms), len(rooms[0])
+        EMPTY, GATE = 2*31-1, 0
+        q = collections.deque()
+        for i in range(row):
+            for j in range(col):
+                if rooms[i][j] == GATE:
+                    q.append((i,j))
+        while q:
+            i,j = q.popleft()
+            for dx,dy in (1,0), (-1,0), (0,1), (0,-1):
+                x,y = i+dx, j+dy
+                if 0<=x<row and 0<=y<col and rooms[i][j] + 1 < rooms[x][y]:
+                    rooms[x][y] = rooms[i][j] + 1
+                    q.append((x,y))
+
+# Time: O(row * col)
+# Space: O(cnt_GATE + cnt_EMPTY)