<p>Given a 2D&nbsp;<code>grid</code> consists of <code>0s</code> (land)&nbsp;and <code>1s</code> (water).&nbsp; An <em>island</em> is a maximal 4-directionally connected group of <code><font face="monospace">0</font>s</code> and a <em>closed island</em>&nbsp;is an island <strong>totally</strong>&nbsp;(all left, top, right, bottom) surrounded by <code>1s.</code></p>

<p>Return the number of <em>closed islands</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<p><img alt="" src="https://assets.leetcode.com/uploads/2019/10/31/sample_3_1610.png" style="width: 240px; height: 120px;" /></p>

<pre>
<strong>Input:</strong> grid = [[1,1,1,1,1,1,1,0],[1,0,0,0,0,1,1,0],[1,0,1,0,1,1,1,0],[1,0,0,0,0,1,0,1],[1,1,1,1,1,1,1,0]]
<strong>Output:</strong> 2
<strong>Explanation:</strong> 
Islands in gray are closed because they are completely surrounded by water (group of 1s).</pre>

<p><strong class="example">Example 2:</strong></p>

<p><img alt="" src="https://assets.leetcode.com/uploads/2019/10/31/sample_4_1610.png" style="width: 160px; height: 80px;" /></p>

<pre>
<strong>Input:</strong> grid = [[0,0,1,0,0],[0,1,0,1,0],[0,1,1,1,0]]
<strong>Output:</strong> 1
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> grid = [[1,1,1,1,1,1,1],
&nbsp;              [1,0,0,0,0,0,1],
&nbsp;              [1,0,1,1,1,0,1],
&nbsp;              [1,0,1,0,1,0,1],
&nbsp;              [1,0,1,1,1,0,1],
&nbsp;              [1,0,0,0,0,0,1],
               [1,1,1,1,1,1,1]]
<strong>Output:</strong> 2
</pre>

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

<ul>
	<li><code>1 &lt;= grid.length, grid[0].length &lt;= 100</code></li>
	<li><code>0 &lt;= grid[i][j] &lt;=1</code></li>
</ul>

def is_open(m: int, n: int, i: int, j: int) -> bool:
    return i == 0 or i == m - 1 or j == 0 or j == n - 1

def get_adj(grid: List[List[int]], m: int, n: int, i: int, j: int) -> List[List[int]]:
    candidates = [(i - 1, j), (i + 1, j), (i, j + 1), (i, j - 1)]
    candidates = [(ii, jj) for (ii, jj) in candidates if ii >= 0 and ii < m and jj >= 0 and jj < n]
    candidates = [(ii, jj) for (ii, jj) in candidates if grid[ii][jj] == 0]
    return candidates

class Solution:
    def closedIsland(self, grid: List[List[int]]) -> int:
        m = len(grid)
        n = len(grid[0])
        num_closed_islands = 0
        start = [(i, j) for i in range(m) for j in range(n) if grid[i][j] == 0]
        visited = set()
        for (start_i, start_j) in start:
            if (start_i, start_j) in visited:
                continue
            to_visit = [(start_i, start_j)]
            island_is_open = False
            while len(to_visit) > 0:
                i, j = to_visit.pop()
                if (i, j) in visited:
                    continue
                visited.add((i, j))
                if is_open(m, n, i, j):
                    island_is_open = True
                to_visit.extend(get_adj(grid, m, n, i, j))
            if not island_is_open:
                num_closed_islands += 1
        return num_closed_islands
18200