<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 {
    void bfs(vector<vector<int>> &vis,vector<vector<int>> &grid,int I,int J){
        int m=grid.size();
        int n=grid[0].size();
        int di[]={-1,0,1,0};
        int dj[]={0,1,0,-1};
        queue<pair<int,int>> q;
        q.push({I,J});
        while (!q.empty()){
            int row=q.front().first;
            int col=q.front().second;
            q.pop();
            for (int i=0;i<4;i++){
                int nrow=row+di[i];
                int ncol=col+dj[i];
                if (nrow>=0 && ncol>=0 && nrow<m && ncol<n && !grid[nrow][ncol] && !vis[nrow][ncol]){
                    vis[nrow][ncol]=1;
                    q.push({nrow,ncol});
                }
            }
        }
    }
public:
    int closedIsland(vector<vector<int>>& grid) {
        queue<pair<int,int>> q;
        int m=grid.size();
        int n=grid[0].size();
        vector<vector<int>> vis(m,vector<int>(n,0));
        for (int j=0;j<n;j++){
            if (!grid[0][j] && !vis[0][j]){
                bfs(vis,grid,0,j);
            }
            if (!grid[m-1][j] && !vis[m-1][j]){
                bfs(vis,grid,m-1,j);
            }
        }
        for (int i=0;i<m;i++){
            if (!grid[i][0] && !vis[i][0]){
                bfs(vis,grid,i,0);
            }
            if (!grid[i][n-1] && !vis[i][n-1]){
                bfs(vis,grid,i,n-1);
            }
        }
        int cnt=0;
        for (int i=1;i<m-1;i++){
            for (int j=1;j<n-1;j++){
                if (!grid[i][j] && !vis[i][j]) {
                    bfs(vis,grid,i,j);
                    cnt++;
                }
            }
        }
        return cnt;
    }
};
18141