Create 01_matrix.py

Author: erjan

01_matrix.py

@@ -0,0 +1,39 @@
+'''
+Given an m x n binary matrix mat, return the distance of the nearest 0 for each cell.
+
+The distance between two adjacent cells is 1.
+'''
+
+class Solution:
+    def updateMatrix(self, mat: List[List[int]]) -> List[List[int]]:
+        DEFAULT = -1
+        queue = []
+        result = [[DEFAULT] * len(mat[0]) for _ in range(len(mat))]
+        for r in range(len(mat)):
+            for c in range(len(mat[0])):
+                if mat[r][c] == 0:
+                    queue.append((r, c, 0)) # depth is 0. i.e. 0 steps to get to this 0
+                    result[r][c] = 0
+                    
+        visited = set()
+        while queue:
+            row, col, depth = queue.pop(0)
+            
+            if (row, col) in visited:
+                continue
+                
+            visited.add((row, col))
+            if result[row][col] == DEFAULT: # no other 0 has gotten here first
+                result[row][col] = depth
+                
+            # if in bounds, not visited, and no result from another 0 yet
+            if row > 0 and (row - 1, col) not in visited and result[row - 1][col] == DEFAULT:
+                queue.append((row - 1, col, depth + 1))
+            if row < len(mat) - 1 and (row + 1, col) not in visited and result[row + 1][col] == DEFAULT:
+                queue.append((row + 1, col, depth + 1))
+            if col > 0 and (row, col - 1) not in visited and result[row][col - 1] == DEFAULT:
+                queue.append((row, col - 1, depth + 1))
+            if col < len(mat[0]) - 1 and (row, col + 1) not in visited and result[row][col + 1] == DEFAULT:
+                queue.append((row, col + 1, depth + 1))
+                
+        return result