<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 dfs(vector<vector<int>>& vis, vector<vector<int>>& grid, int row, int col){
        int n = grid.size();
        int m = grid[0].size();
        if(row < 0 || row == n || col == m || col < 0 || vis[row][col]) return;
        vis[row][col] = 1;

        if(row + 1 < n && grid[row+1][col] == 1 && vis[row+1][col] == 0){
            dfs(vis,grid,row+1,col);
        }
        if(row - 1 >= 0 && grid[row-1][col] == 1 && vis[row-1][col] == 0){
            dfs(vis,grid,row-1,col);
        }
        if(col + 1 < m && grid[row][col+1] == 1 && vis[row][col+1] == 0){
            dfs(vis,grid,row,col+1);
        }
        if(col - 1 >= 0 && grid[row][col-1] == 1 && vis[row][col-1] == 0){
            dfs(vis,grid,row,col-1);
        }
    }

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

        int ct = 0;
        for(int i=0;i<n;i++){
            for(int j=0;j<m;j++){
                if(grid[i][j] == 1 && vis[i][j] == 0) ct++;
            }
        }

        return ct;
    }
};
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