<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 x[4]={-1,1,0,0};
    int y[4]={0,0,-1,1};
    bool check(int i,int j,int n,int m){
        if(i<0 || j<0 || i>=n || j>=m)return false;
        return true;
    }
    void dfs(int i, int j,vector<vector<int>>& grid,vector<vector<int>>& vis, int&count,bool&boundary ){
        if( !check(i,j,grid.size(),grid[0].size()) || vis[i][j] || grid[i][j]==0)return;
        vis[i][j]=true;
        if(i==0 || i==grid.size()-1 || j==0 || j==grid[0].size()-1)boundary=true;
        count++;
        for(int it=0;it<4;it++){
            dfs(i+x[it],j+y[it],grid,vis,count,boundary);
        }
    }
    int numEnclaves(vector<vector<int>>& grid) {
        int safecells=0,rows=grid.size(),columns=grid[0].size();
        int n=rows,m=columns;
        vector<vector<int>>vis(rows,vector<int>(columns));
        int ans=0;
        for(int i=0;i<rows;i++){
            for(int j=0;j<columns;j++){
                if(!vis[i][j] && grid[i][j]!=0){
                    int count=0;bool boundary=false;
                    // dfs(i,j,grid,vis,count,boundary);
                    queue<pair<int,int>>q;
                    q.push({i,j});
                    while(!q.empty()){
                        int ii=q.front().first,jj=q.front().second;
                        q.pop();
                        if(vis[ii][jj] )continue;
                        vis[ii][jj]=1;count++;
                        if(ii==0||ii==n-1||jj==0||jj==m-1)boundary=true;
                        for(int k=0;k<4;k++){
                            if(!check(ii+x[k],jj+y[k],n,m) || grid[ii+x[k]][jj+y[k]]==0)continue;
                            q.push({ii+x[k],jj+y[k]});
                        }
                    }
                    if(!boundary)ans+=count;
                }
            }
        }
        return ans;
    }
};
56367