<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:

void bfs(vector<vector<int>>& grid,vector<vector<int>>&visited,int x,int y)
{
    int n=grid.size();
    int m=grid[0].size();
    queue<pair<int,int>>q;
    q.push({x,y});
    visited[x][y]=1;
    while(!q.empty())
    {
        int cr=q.front().first;
        int cc=q.front().second;
        q.pop();
        for(int i=-1;i<=1;i++)
        {
            for(int j=-1;j<=1;j++)
            {
                if(i==0 || j==0)
                {
                    int nr=cr+i;
                    int nc=cc+j;
                    if((nr>0 && nr<n-1) && 
                    (nc>0 && nc<m-1) && 
                    grid[nr][nc]==0 && 
                    visited[nr][nc]==0)
                    {
                        visited[nr][nc]=1;
                        q.push({nr,nc});
                    }
                }
            }
        }
    }
    return;
}
void block(vector<vector<int>>& grid,vector<vector<int>>&visited)
{
    int n=grid.size();
    int m=grid[0].size();
    queue<pair<int,int>>q;
    for(int i=0;i<n;i++)
    {
        if(grid[i][0]==0)
        {
            visited[i][0]=1;
            q.push({i,0});
            grid[i][0]=2;
        }
        if(grid[i][m-1]==0)
        {
            visited[i][m-1]=1;
            q.push({i,m-1});
            grid[i][m-1]=2;
        }
    }
     for(int j=0;j<m;j++)
    {
        if(grid[0][j]==0)
        {
            visited[0][j]=1;
            q.push({0,j});
            grid[0][j]=2;
        }
        if(grid[n-1][j]==0)
        {
            visited[n-1][j]=1;
            q.push({n-1,j});
            grid[n-1][j]=2;
        }
    }
    while(!q.empty())
    {
        int x=q.front().first;
        int y=q.front().second;
        q.pop();
        for(int i=-1;i<=1;i++)
        {
            for(int j=-1;j<=1;j++)
            {
                if(i==0 || j==0)
                {
                    int nr=x+i;
                    int nc=y+j;
                    if((nr>=0 && nr<n) && 
                    (nc>=0 && nc<m) && 
                    grid[nr][nc]==0 && 
                    visited[nr][nc]==0)
                    {
                        grid[nr][nc]=2;
                        visited[nr][nc]=1;
                        q.push({nr,nc});
                    }
                }
            }
        }
    }
    return;
    
}
    int closedIsland(vector<vector<int>>& grid) {
        int n=grid.size();
        int m=grid[0].size();
        vector<vector<int>>visited(n,vector<int>(m,0));
        block(grid,visited);
        int ct=0;
        for(int i=1;i<n-1;i++)
        {
            for(int j=1;j<m-1;j++)
            {
                if(visited[i][j]==0 && grid[i][j]==0)
                {
                    ct++;
                    bfs(grid,visited,i,j);
                }
            }
        }
        return ct;
    }
};
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