<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:
    int closedIsland(vector<vector<int>>& grid) {
        int n = grid.size();
        int m = grid[0].size();
        int count = 0;
        int si[] = {0,-1,0,1};  
        int sj[] = {-1,0,1,0};  
        vector<vector<bool>> vis(n,vector(m,false));

        for(int i = 0; i < n; i++){
            for(int j = 0; j < m; j++){
                if(grid[i][j] == 1 || vis[i][j]){   
                    continue;
                }
                queue<pair<int,int>> qu;
                qu.push({i,j});
                bool valid = true;
                while(!qu.empty()){
                    pair<int,int> par = qu.front();
                    qu.pop();
                    for(int d=0;d<4;d++){
                        int ci = par.first + si[d];
                        int cj = par.second + sj[d];                        
                        if(ci < 0 || ci >= n || cj < 0 || cj >= m){   
                            valid = false;
                            continue;
                        }
                        if(grid[ci][cj] == 1){
                            continue;
                        }   
                        if(vis[ci][cj]){
                            continue;
                        }  
                        qu.push({ci, cj});
                        vis[ci][cj] = true;  
                    }                    
                }  
                if(valid){
                    count++; 
                }
            }
        }
        return count;         
    }
};
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