<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>

vector<int> ver = {1, -1, 0, 0};
vector<int> hor = {0, 0, 1, -1};
vector<vector<int>> vis(501, vector<int> (501, 0));
int cnt = 0;
class Solution {
public:
    int numEnclaves(vector<vector<int>>& grid) {
        int n = grid.size();
        int m = grid[0].size();
        int ans = 0;
        for (int i = 0; i < n; i++)
        {
            for (int j = 0; j < m; j++)
            {
                vis[i][j] = 0;
            }
        }
        for (int i = 0; i < n; i++)
        {
            for (int j = 0; j < m; j++)
            {
                if (grid[i][j] && !vis[i][j])
                {
                    cnt = 0;
                    bool dead = dfs(grid, i, j, n, m);
                    if (!dead)
                    {
                        ans += cnt;
                    }
                }
            }
        }
        return ans;
    }
    bool isvalid(int i, int j, int n, int m, vector<vector<int>> &vis)
    {
        if (i < 0 || j < 0 || i >= n || j >= m || vis[i][j])
        {
            return 0;
        }
        return 1;
    }
    bool isdead(int i, int j, int n, int m)
    {
        if (i == 0 || j == 0 || i == n-1 || j == m-1)
        {
            return 1;
        }
        return 0;
    }
    bool dfs(vector<vector<int>> &board, int i, int j, int n, int m)
    {
        vis[i][j] = 1;
        cnt++;
        bool dead = 0;
        if (isdead(i, j, n, m))
        {
            dead = 1;
        }
        for (int d = 0; d < 4; d++)
        {
            int a = i + ver[d], b = j + hor[d];
            if (isvalid(a, b, n, m, vis) && board[a][b])
            {
                dead = (dead | dfs(board, a, b, n, m));
            }
        }
        return dead;
    }
};
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