<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 rows = grid.size();
        int cols = grid[0].size();
        int count = 0;
        set<pair<int,int>> visited;

        for(int r = 0; r < rows; r++)
        {
            for(int  c = 0; c < cols; c++)
            {
                if(grid[r][c] == 0 && (r == 0 || c == 0 || r == rows - 1 || c == cols - 1))
                    dfs(grid,visited,r,c,rows,cols);
            }
        }

        for(int r = 0; r < rows; r++)
        {
            for(int  c = 0; c < cols; c++)
            {
                if(grid[r][c] == 0 && !visited.count({r,c}))
                {
                    count++;
                    dfs(grid,visited,r,c,rows,cols);
                }
            }
        }
        return count;
    }

    void dfs(vector<vector<int>>& grid, set<pair<int,int>>& visited, int r, int c, int rows, int cols)
    {
        if(r < 0 || c < 0 || r >= rows || c >= cols || grid[r][c] != 0 || visited.count({r,c}))
            return;
        
        visited.insert({r,c});

        dfs(grid,visited,r+1,c,rows,cols);
        dfs(grid,visited,r-1,c,rows,cols);
        dfs(grid,visited,r,c+1,rows,cols);
        dfs(grid,visited,r,c-1,rows,cols);
    }
};
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