<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 {
    vector<vector<int>> dir={{1,0},{0,1},{-1,0},{0,-1}};
    void bfs(vector<vector<int>>& a, int i, int j){
        auto m = a.size(), n=a[0].size();
        queue<vector<int>> q;
        q.push({i,j});
        a[i][j]=1;
        while(!q.empty()){
            auto e = q.front();
            q.pop();
            for(auto d : dir){
                i=d[0]+e[0];
                j=d[1]+e[1];
                if(i < 0 || j < 0 ||i == m|| j==n|| a[i][j]!=0)
                    continue;
                a[i][j]=1;
                q.push({i,j});
            }
        }
    }
public:
    int closedIsland(vector<vector<int>>& a) {
        auto m = a.size(), n=a[0].size();
        for(int i=0; i < m; i++){
            if(a[i][n-1]==0)
                bfs(a,i,n-1);
            if(a[i][0]==0)
                bfs(a,i,0);
        }
        for(int i=0; i < n; i++){
            if(a[m-1][i]==0)
                bfs(a,m-1,i);
            if(a[0][i]==0)
               bfs(a,0,i);
        }
        int res=0;
        for(int i = 0; i < m; i++){
            for(int j = 0; j < n; j++){
                if(a[i][j]==0){
                    res++;
                    bfs(a,i,j);
                }
            }
        }
        return res;
    }
};
23528