<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:
    int n, m;
    bool isValid(int r, int c){
        if(r<0 || c<0 || r>=n || c>=m){
            return false;
        }
        return true;
    }
    void dfs(vector<vector<int>>& grid, vector<vector<bool>>& vis, int r, int c){
        vis[r][c] = true;
        if(isValid(r, c+1) && !vis[r][c+1] && grid[r][c+1]==1){
            dfs(grid, vis, r, c+1);
        }
        if(isValid(r, c-1) && !vis[r][c-1] && grid[r][c-1]==1){
            dfs(grid, vis, r, c-1);
        }
        if(isValid(r+1, c) && !vis[r+1][c] && grid[r+1][c]==1){
            dfs(grid, vis, r+1, c);
        }
        if(isValid(r-1, c) && !vis[r-1][c] && grid[r-1][c]==1){
            dfs(grid, vis, r-1, c);
        }
    }
    int numEnclaves(vector<vector<int>>& grid) {
        n = grid.size();
        m = grid[0].size();
        vector<vector<bool>> vis(n, vector<bool>(m, false));
        for(int i = 0;i<n;i++){
            if(grid[i][0] == 1 && !vis[i][0]){
                dfs(grid, vis, i, 0);
            }
            if(grid[i][m-1] == 1 && !vis[i][m-1]){
                dfs(grid, vis, i, m-1);
            }
        }
        for(int i = 0;i<m;i++){
            if(grid[0][i] == 1 && !vis[0][i]){
                dfs(grid, vis, 0, i);
            }
            if(grid[n-1][i] == 1 && !vis[n-1][i]){
                dfs(grid, vis, n-1, i);
            }
        }
        int count = 0;
        for(int i = 0;i<n; i++){
            for(int j = 0;j<m;j++){
                if(!vis[i][j] && grid[i][j]==1){
                    count++;
                }
            }
        }
        return count;
    }
};
52132