<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 {
public:
    void markEverything(vector<vector<int>>& grid, int x, int y)
    {
        if (grid[x][y] != 1)
            return;
        
        grid[x][y] = 0;
        queue<pair<int, int>> q;
        q.push({x, y});

        while (!q.empty())
        {
            auto& pos = q.front();

            vector<int> xAdd({-1, 1, 0, 0});
            vector<int> yAdd({0, 0, 1, -1});

            for (int i = 0; i < xAdd.size(); i++)
            {
                if (((pos.first + xAdd[i]) >= 0) && 
                    ((pos.first + xAdd[i]) < (grid.size())) && 
                    ((pos.second + yAdd[i]) < (grid[0].size())) &&
                    ((pos.second + yAdd[i]) >= 0) &&
                    ((grid[pos.first + xAdd[i]][pos.second + yAdd[i]] == 1)))
                {
                    grid[pos.first + xAdd[i]][pos.second + yAdd[i]] = 0;
                    q.push({pos.first + xAdd[i], pos.second + yAdd[i]});
                }
            }

            q.pop();
        }
    }

    int numEnclaves(vector<vector<int>>& grid) {
        for (int i = 0; i < grid.size(); i++)
        {
            markEverything(grid, i, 0);
            markEverything(grid, i, grid[0].size() - 1);
        }

        for (int i = 0; i < grid[0].size(); i++)
        {
            markEverything(grid, 0, i);
            markEverything(grid, grid.size() - 1, i);
        }

        int c = 0;

        for (int i = 1; i < (grid.size() - 1); i++)
        {
            for (int j = 1; j < (grid[0].size() - 1); j++)
            {
                c += grid[i][j];
            }
        }
        return c;
    }
};
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