<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 dfs(int r,int c,vector<vector<int>>&grid,vector<vector<int>>&vis)
    {
        int n=grid.size();
        int m=grid[0].size();

        vector<int>row={0,0,-1,1};
        vector<int>col={1,-1,0,0};

        vis[r][c]=1;

        for(int i=0;i<4;i++)
        {
            int new_r=r+row[i];
            int new_c=c+col[i];

            if(new_r>=0 && new_r<n && new_c>=0 && new_c<m && grid[new_r][new_c]==0 && vis[new_r][new_c]==0)
            {
                dfs(new_r,new_c,grid,vis);
            }
        }
    }

    int closedIsland(vector<vector<int>>& grid) {
        int n=grid.size();
        int m=grid[0].size();

        vector<vector<int>>vis(n,vector<int>(m,0));

        for(int i=0;i<m;i++)
        {
            if(vis[0][i]==0 && grid[0][i]==0)
            {
                dfs(0,i,grid,vis);
            }

            if(vis[n-1][i]==0 && grid[n-1][i]==0)
            {
                dfs(n-1,i,grid,vis);
            }
        }
        for(int i=0;i<n;i++)
        {
            if(vis[i][0]==0 && grid[i][0]==0)
            {
                dfs(i,0,grid,vis);
            }

            if(vis[i][m-1]==0 && grid[i][m-1]==0)
            {
                dfs(i,m-1,grid,vis);
            }
        }

        int result=0;
        for(int i=0;i<n;i++)
        {
            for(int j=0;j<m;j++)
            {
                if(vis[i][j]==0 && grid[i][j]==0)
                {
                    dfs(i,j,grid,vis);
                    result++;
                }
            }
        }
        return result;
    }
};
16751