<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:
        R, C = len(grid), len(grid[0])

        to_visit = []
        for r in range(R):
            if grid[r][0] == 1:
                to_visit.append((r, 0))
                grid[r][0] = 0
            if grid[r][C - 1] == 1:
                to_visit.append((r, C - 1))
                grid[r][C - 1] = 0
        for c in range(C):
            if grid[0][c] == 1:
                to_visit.append((0, c))
                grid[0][c] = 0
            if grid[R - 1][c] == 1:
                to_visit.append((R - 1, c))
                grid[R - 1][c] = 0

        dr = [0, 1, 0, -1]
        dc = [1, 0, -1, 0]
        while to_visit: 
            r, c = to_visit.pop()
            for i in range(4):
                nr, nc = r + dr[i], c + dc[i]
                if 0 <= nr < R and 0 <= nc < C and grid[nr][nc] == 1:
                    grid[nr][nc] = 0
                    to_visit.append((nr, nc))
        
        return sum([row.count(1) for row in grid])
19801