<p>Given a 2D&nbsp;<code>grid</code> consists of <code>0s</code> (land)&nbsp;and <code>1s</code> (water).&nbsp; An <em>island</em> is a maximal 4-directionally connected group of <code><font face="monospace">0</font>s</code> and a <em>closed island</em>&nbsp;is an island <strong>totally</strong>&nbsp;(all left, top, right, bottom) surrounded by <code>1s.</code></p>

<p>Return the number of <em>closed islands</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<p><img alt="" src="https://assets.leetcode.com/uploads/2019/10/31/sample_3_1610.png" style="width: 240px; height: 120px;" /></p>

<pre>
<strong>Input:</strong> grid = [[1,1,1,1,1,1,1,0],[1,0,0,0,0,1,1,0],[1,0,1,0,1,1,1,0],[1,0,0,0,0,1,0,1],[1,1,1,1,1,1,1,0]]
<strong>Output:</strong> 2
<strong>Explanation:</strong> 
Islands in gray are closed because they are completely surrounded by water (group of 1s).</pre>

<p><strong class="example">Example 2:</strong></p>

<p><img alt="" src="https://assets.leetcode.com/uploads/2019/10/31/sample_4_1610.png" style="width: 160px; height: 80px;" /></p>

<pre>
<strong>Input:</strong> grid = [[0,0,1,0,0],[0,1,0,1,0],[0,1,1,1,0]]
<strong>Output:</strong> 1
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> grid = [[1,1,1,1,1,1,1],
&nbsp;              [1,0,0,0,0,0,1],
&nbsp;              [1,0,1,1,1,0,1],
&nbsp;              [1,0,1,0,1,0,1],
&nbsp;              [1,0,1,1,1,0,1],
&nbsp;              [1,0,0,0,0,0,1],
               [1,1,1,1,1,1,1]]
<strong>Output:</strong> 2
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= grid.length, grid[0].length &lt;= 100</code></li>
	<li><code>0 &lt;= grid[i][j] &lt;=1</code></li>
</ul>

class Solution {
public:
    
    vector<vector<int>> dir{{1,0}, {0,1}, {-1,0}, {0,-1}};
    void bfs(vector<vector<int>>& grid, vector<vector<bool>>& vis, int i, int j){
        
        int m=grid.size();
        int n=grid[0].size();
        queue<pair<int,int>> q;
        q.push({i, j});
        vis[i][j]=true;



        while(!q.empty()){
            pair<int,int> node=q.front();
            q.pop();
            for(auto it: dir){
                int i_=node.first+it[0];
                int j_=node.second+it[1];

                if((i_>=0 && i_<m) && (j_>=0 && j_<n) && (grid[i_][j_]==0) && (!vis[i_][j_])){
                    q.push({i_, j_});
                    vis[i_][j_]=true;
                }
            }
        }
        return;
    }
    


        int closedIsland(vector<vector<int>>& grid) {
        
        int m=grid.size();
        int n=grid[0].size();

        
        vector<vector<bool>> vis(m, vector<bool>(n, false));
        
        
        //First Column:
        for(int i=0; i<m; i++){
            if(grid[i][0]==0)
                bfs(grid,vis,i,0);
        }

        //Last Column:
        for(int i=0; i<m; i++){
            if(grid[i][n-1]==0)
                bfs(grid,vis,i,n-1);
        }

        //first row:
        for(int i=0; i<n; i++){
            if(grid[0][i]==0)
                bfs(grid,vis,0,i);
        }

        //last row:
        for(int i=0; i<n; i++){
            if(grid[m-1][i]==0)
                bfs(grid,vis,m-1,i);
        }

        int count=0;
        for(int i=0; i<m; i++){
            for(int j=0; j<n; j++){
                if((grid[i][j]==0) && !vis[i][j]){
                    bfs(grid, vis, i, j);
                    count++;
                }
            }
        }

        return count;

    }
};
22833