<p>You are given two <code>m x n</code> binary matrices <code>grid1</code> and <code>grid2</code> containing only <code>0</code>&#39;s (representing water) and <code>1</code>&#39;s (representing land). An <strong>island</strong> is a group of <code>1</code>&#39;s connected <strong>4-directionally</strong> (horizontal or vertical). Any cells outside of the grid are considered water cells.</p>

<p>An island in <code>grid2</code> is considered a <strong>sub-island </strong>if there is an island in <code>grid1</code> that contains <strong>all</strong> the cells that make up <strong>this</strong> island in <code>grid2</code>.</p>

<p>Return the <em><strong>number</strong> of islands in </em><code>grid2</code> <em>that are considered <strong>sub-islands</strong></em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/06/10/test1.png" style="width: 493px; height: 205px;" />
<pre>
<strong>Input:</strong> grid1 = [[1,1,1,0,0],[0,1,1,1,1],[0,0,0,0,0],[1,0,0,0,0],[1,1,0,1,1]], grid2 = [[1,1,1,0,0],[0,0,1,1,1],[0,1,0,0,0],[1,0,1,1,0],[0,1,0,1,0]]
<strong>Output:</strong> 3
<strong>Explanation: </strong>In the picture above, the grid on the left is grid1 and the grid on the right is grid2.
The 1s colored red in grid2 are those considered to be part of a sub-island. There are three sub-islands.
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/06/03/testcasex2.png" style="width: 491px; height: 201px;" />
<pre>
<strong>Input:</strong> grid1 = [[1,0,1,0,1],[1,1,1,1,1],[0,0,0,0,0],[1,1,1,1,1],[1,0,1,0,1]], grid2 = [[0,0,0,0,0],[1,1,1,1,1],[0,1,0,1,0],[0,1,0,1,0],[1,0,0,0,1]]
<strong>Output:</strong> 2 
<strong>Explanation: </strong>In the picture above, the grid on the left is grid1 and the grid on the right is grid2.
The 1s colored red in grid2 are those considered to be part of a sub-island. There are two sub-islands.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>m == grid1.length == grid2.length</code></li>
	<li><code>n == grid1[i].length == grid2[i].length</code></li>
	<li><code>1 &lt;= m, n &lt;= 500</code></li>
	<li><code>grid1[i][j]</code> and <code>grid2[i][j]</code> are either <code>0</code> or <code>1</code>.</li>
</ul>

class Solution:
    def countSubIslands(self, grid1: List[List[int]], grid2: List[List[int]]) -> int:
        row = len(grid2) # rows in grid2
        col = len(grid2[0]) # cols in grid2

        def recursive_island(grid, idx1, idx2, row, col, island=[]):
            # Append the current positio to the island list and mark it as visited
            island.append([idx1, idx2])
            grid[idx1][idx2] = 0

            # check and recurse to the right
            if idx2 + 1 < col and grid[idx1][idx2 + 1]:
                recursive_island(grid, idx1, idx2 + 1, row, col, island)
            # check and recurse to the up
            if idx1 - 1 >= 0 and grid[idx1 - 1][idx2]:
                recursive_island(grid, idx1 - 1, idx2, row, col, island)
            # check and recurse to the down
            if idx1 + 1 < row and grid[idx1 + 1][idx2]:
                recursive_island(grid, idx1 + 1, idx2, row, col, island)
            # check and recurse to the left
            if idx2 - 1 >= 0 and grid[idx1][idx2 - 1]:
                recursive_island(grid, idx1, idx2 - 1, row, col, island)

        def all_sub_islands(grids):
            all_island = []
            for idx1, grids in enumerate(grid2):
                for idx2, is_island in enumerate(grids):
                    island = []
                    if is_island:
                        recursive_island(grid2, idx1, idx2, row, col, island)
                        all_island.append(island)
            return (all_island)

        def num_of_sub_islands(grid):
            x = 0
            for islands in all_sub_islands(grid):
                for subIsland in islands:
                    if not grid1[subIsland[0]][subIsland[1]]:
                        break
                else:
                    x += 1
            return x
        return num_of_sub_islands(grid2)


1921