<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, queue<pair<int, int>>&q){
        int n = grid.size();
        int m = grid[0].size();
        while(!q.empty()){
            pair<int, int> top = q.front();
            int x = top.first;
            int y = top.second;
            grid[x][y]=-1;
            q.pop();
            if(x+1<n && grid[x+1][y]==0)q.push({x+1, y});
            if(x-1>=0 && grid[x-1][y]==0)q.push({x-1, y});
            if(y+1<m && grid[x][y+1]==0)q.push({x, y+1});
            if(y-1>=0 && grid[x][y-1]==0)q.push({x, y-1});
        }
    }
    
    int closedIsland(vector<vector<int>>& grid) {
       int n=grid.size();
       int m= grid[0].size();
       queue<pair<int, int>>q;
       for(int j=0; j<m; ++j){
            if(grid[0][j]==0)q.push({0, j});
            if(grid[n-1][j]==0)q.push({n-1, j});
       } 
       for(int i=0; i<n; ++i){
            if(grid[i][0]==0)q.push({i, 0});
            if(grid[i][m-1]==0)q.push({i, m-1});
       } 
       bfs(grid, q);
       int ans = 0;
       for(int i=0; i<n; ++i){
            for(int j=0; j<m; ++j){
                if(grid[i][j]==0){
                    q.push({i, j});
                    bfs(grid, q);
                    ans++;
                }
            }
       }
       return ans;
    }
};
14666