<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) 
    {
        if(grid.size() == 0)
            return 0;
        
        int num_closed_islands = 0;
        int num_rows = grid.size(), num_columns = grid[0].size(), r1, c1, r, c, ele;
    
        for(r = 0; r < num_rows; r++)
            for(c = 0; c < num_columns; c++)
                if(grid[r][c] == 0)
                {
                    bool closed = true;
                    
                    grid[r][c] = 1;
                    queue <int> neighbours;
                    neighbours.push(r*num_columns + c);
                    
                    while(!neighbours.empty())
                    {
                        ele = neighbours.front();
                        neighbours.pop();
                        r1 = ele / num_columns;
                        c1 = ele % num_columns;
                        
                        if(r1 == 0 or c1 == 0 or r1 == num_rows-1 or c1 == num_columns-1)
                            closed = false;
                        
                        if(r1-1 >= 0 and grid[r1-1][c1] == 0)
                        {
                            neighbours.push((r1-1)*num_columns + c1);
                            grid[r1-1][c1] = 1;
                        }
                        if(r1+1 < num_rows and grid[r1+1][c1] == 0)
                        {
                            neighbours.push((r1+1)*num_columns + c1);
                            grid[r1+1][c1] = 1;
                        }
                        if(c1-1 >= 0 and grid[r1][c1-1] == 0)
                        {
                            neighbours.push(r1*num_columns + c1-1);
                            grid[r1][c1-1] = 1;
                        }
                        if(c1+1 < num_columns and grid[r1][c1+1] == 0)
                        {
                            neighbours.push(r1*num_columns + c1+1);
                            grid[r1][c1+1] = 1;
                        }
                    }
                    
                    if(closed)
                        num_closed_islands++;
                }
        
        return num_closed_islands;
    }
};
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