<p>You are given an <code>m x n</code> binary matrix <code>grid</code>, where <code>0</code> represents a sea cell and <code>1</code> represents a land cell.</p>

<p>A <strong>move</strong> consists of walking from one land cell to another adjacent (<strong>4-directionally</strong>) land cell or walking off the boundary of the <code>grid</code>.</p>

<p>Return <em>the number of land cells in</em> <code>grid</code> <em>for which we cannot walk off the boundary of the grid in any number of <strong>moves</strong></em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/02/18/enclaves1.jpg" style="width: 333px; height: 333px;" />
<pre>
<strong>Input:</strong> grid = [[0,0,0,0],[1,0,1,0],[0,1,1,0],[0,0,0,0]]
<strong>Output:</strong> 3
<strong>Explanation:</strong> There are three 1s that are enclosed by 0s, and one 1 that is not enclosed because its on the boundary.
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/02/18/enclaves2.jpg" style="width: 333px; height: 333px;" />
<pre>
<strong>Input:</strong> grid = [[0,1,1,0],[0,0,1,0],[0,0,1,0],[0,0,0,0]]
<strong>Output:</strong> 0
<strong>Explanation:</strong> All 1s are either on the boundary or can reach the boundary.
</pre>

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

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

class Solution:
    def numEnclaves(self, grid: List[List[int]]) -> int:
        visited = set()

        def dfs(row, col):
            if row < 0 or col < 0:
                return
            if row > len(grid) - 1 or col > len(grid[0]) - 1:
                return
            if grid[row][col] != 1:
                return

            grid[row][col] = 0
            neighbors = (
                (row - 1, col), # Top
                (row + 1, col), # Bot
                (row, col + 1), # Left
                (row, col - 1), # Right
            )
            for row, col in neighbors:
                dfs(row, col)


        # Visit border lands
        for row in range(len(grid)):
            if grid[row][0] == 1:
                dfs(row, 0)
            if grid[row][len(grid[0]) - 1]:
                dfs(row, len(grid[0]) - 1)
        for col in range(len(grid[0])):
            if grid[0][col] == 1:
                dfs(0, col)
            if grid[len(grid) - 1][col]:
                dfs(len(grid) - 1, col)

        # Count number of unvisited lands
        n_enclaves = 0
        for row in range(1, len(grid) - 1):
            for col in range(1, len(grid[0]) - 1):
                if grid[row][col]:
                    n_enclaves += 1
                    
        return n_enclaves
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