Count Sub Islands LeetCode solution in Python

1
class Solution(object):
2
    def countSubIslands(self, grid1, grid2):
3
        m = len(grid1)
4
        n = len(grid1[0])
5

6
        def dfs(i, j):
7
            if i < 0 or i >= m or j < 0 or j >= n or grid2[i][j] == 0:
8
                return
9
            grid2[i][j] = 0
10
            dfs(i + 1, j)
11
            dfs(i - 1, j)
12
            dfs(i, j + 1)
13
            dfs(i, j - 1)
14

15
        # here we remove the unnecesaary islands by seeing the point that if for a land in grid2 and water in grid1 it cannot be a subisland and hence island in which this land resides should be removed
16
        for i in range(m):
17
            for j in range(n):
18
                if grid2[i][j] == 1 and grid1[i][j] == 0:
19
                    dfs(i, j)
20
        # now we just need to count the islands left over
21
        count = 0
22
        for i in range(m):
23
            for j in range(n):
24
                if grid2[i][j] == 1:
25

26
                    dfs(i, j)
27
                    count += 1
28
        return count