<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(int row,int col,vector<vector<int>>& visited,vector<vector<int>>& grid,int& flag){
        vector<int> dx={1,0,-1,0};
        vector<int> dy={0,1,0,-1};
        int n=grid.size();
        int m=grid[0].size();
        queue<pair<int,int>> q;
        q.push({row,col});
        visited[row][col]=1;
        while(!q.empty()){
            int r=q.front().first;
            int c=q.front().second;
            if(r==n-1 || r==0 || c==m-1 || c==0) flag=1;
            q.pop();
            for(int i=0;i<4;i++){
                int newrow=r+dx[i];
                int newcol=c+dy[i];
                if(newrow>=0 && newrow<n && newcol>=0 && newcol<m && grid[newrow][newcol]==0 && visited[newrow][newcol]==0){
                    q.push({newrow,newcol});
                    visited[newrow][newcol]=1;
                }
            }
        }
    }
    int closedIsland(vector<vector<int>>& grid) {
        int ans=0;
        int n=grid.size(),m=grid[0].size();
        vector<vector<int>> visited(n,vector<int>(m,0));
        for(int i=0;i<n;i++){
            for(int j=0;j<m;j++){
                if(grid[i][j]==0 && visited[i][j]==0){
                    int flag=0;
                    bfs(i,j,visited,grid,flag);
                    if(flag==0) ans++;
                }
            }
        }
        return ans;
    }
};
18489