1020 Number of Enclaves.py

Author: rajeevranjancom

1020 Number of Enclaves.py

@@ -0,0 +1,98 @@
+#!/usr/bin/python3
+"""
+Given a 2D array A, each cell is 0 (representing sea) or 1 (representing land)
+
+A move consists of walking from one land square 4-directionally to another land
+square, or off the boundary of the grid.
+
+Return the number of land squares in the grid for which we cannot walk off the
+boundary of the grid in any number of moves.
+
+Example 1:
+Input: [[0,0,0,0],[1,0,1,0],[0,1,1,0],[0,0,0,0]]
+Output: 3
+Explanation:
+There are three 1s that are enclosed by 0s, and one 1 that isn't enclosed
+because its on the boundary.
+
+Example 2:
+Input: [[0,1,1,0],[0,0,1,0],[0,0,1,0],[0,0,0,0]]
+Output: 0
+Explanation:
+All 1s are either on the boundary or can reach the boundary.
+
+Note:
+1 <= A.length <= 500
+1 <= A[i].length <= 500
+0 <= A[i][j] <= 1
+All rows have the same size.
+"""
+from typing import List
+
+
+dirs = ((0, -1), (0, 1), (1, 0), (-1, 0))
+
+
+class Solution:
+    def numEnclaves(self, A: List[List[int]]) -> int:
+        """
+        not dfs from any cell, but dfs from the edges
+        """
+        m, n = len(A), len(A[0])
+        visited = [[False for _ in range(n)] for _ in range(m)]
+        for i in range(m):
+            for j in range(n):
+                if not visited[i][j] and A[i][j] == 1 and (i == 0 or j == 0 or i == m - 1 or j == n - 1):
+                    self.dfs(A, i, j, visited)
+
+        ret = 0
+        for i in range(m):
+            for j in range(n):
+                if A[i][j] == 1 and not visited[i][j]:
+                    ret += 1
+        return ret
+
+    def dfs(self, A, i, j, visited):
+        m, n = len(A), len(A[0])
+        visited[i][j] = True
+        for di, dj in dirs:
+            I = i + di
+            J = j + dj
+            if 0 <= I < m and 0 <= J < n and not visited[I][J] and A[I][J] == 1:
+                self.dfs(A, I, J, visited)
+
+
+class SolutionError:
+    def __init__(self):
+        self.ret = 0
+
+    def numEnclaves(self, A: List[List[int]]) -> int:
+        """
+        dfs coloring
+        """
+        m, n = len(A), len(A[0])
+        visited = [[None for _ in range(n)] for _ in range(m)]  # 0 not off, 1 off
+        for i in range(m):
+            for j in range(n):
+                if not visited[i][j] and A[i][j] == 1:
+                    self.dfs(A, i, j, visited)
+        return self.ret
+
+    def dfs(self, A, i, j, visited):
+        m, n = len(A), len(A[0])
+        visited[i][j] = 0
+        for di, dj in dirs:
+            I = i + di
+            J = j + dj
+            if not (0 <= I < m and 0 <= J < n):
+                visited[i][j] = 1
+                return True
+            if visited[I][J] == 1:
+                visited[i][j] = 1
+                return True
+            if visited[I][J] is None and A[I][J] == 1 and self.dfs(A, I, J, visited):
+                visited[i][j] = 1
+                return True
+
+        self.ret += 1
+        return False