<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:
    bool valid(int ci, int cj, int r, int c, vector<vector<int>>& grid)
    {
        if(ci < 0 || ci >= r || cj < 0 || cj >= c || grid[ci][cj] == 1)
        {
            return false;
        }
        return true;
    }
    
    void dfs(int si,int sj, int r, int c, vector<vector<int>>& grid)
    {
        grid[si][sj] = 1;

        vector<pair<int,int>> d = {{0,1},{0,-1},{-1,0},{1,0}};

        for(int i=0;i<4;i++)
        {
            int ci = si + d[i].first;
            int cj = sj + d[i].second;

            if(valid(ci,cj,r,c,grid))
            {
                dfs(ci,cj,r,c,grid);
            }
        }
    }
    
    int closedIsland(vector<vector<int>>& grid) {
        int r = grid.size();
        int c = grid[0].size();

        for(int i=0;i<r;i++)
        {
            for(int j=0;j<c;j++)
            {
                if(i*j==0 || i==r-1 || j==c-1)
                {
                    if(grid[i][j]==0)
                    {
                        dfs(i,j,r,c,grid);
                    }
                }
            }
        }

        int cnt = 0;
        for(int i=0;i<r;i++)
        {
            for(int j=0;j<c;j++)
            {
                if(grid[i][j]==0)
                {
                    cnt++;
                    dfs(i,j,r,c,grid);
                }
            }
        }
        return cnt;
    }
};

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