<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:
    vector<int>rows{-1,1,0,0};
    vector<int>cols{0,0,-1,1};
    bool isSafe(int r,int c,int m,int n){
        if(r<0 || r>=m || c<0 || c>=n){
            return false;
        }
        return true;
    }
    void dfs(vector<vector<int>>& grid,int r,int c,int m,int n,vector<vector<bool>>&vis){
        vis[r][c] = true;
        for(int k = 0;k<4;k++){
            int nR = r+rows[k];
            int nC = c+cols[k];
            if( isSafe(nR,nC,m,n) == true && grid[nR][nC] == 0 && vis[nR][nC] == false){
                dfs(grid,nR,nC,m,n,vis);
            }
        }
    }
    int closedIsland(vector<vector<int>>& grid) {
        int m = grid.size();
        int n = grid[0].size();
        vector<vector<bool>>vis(m+1,vector<bool>(n+1,false));
        for(int i=0;i<n;i++){
            if(vis[0][i]==false && grid[0][i]==0){
                dfs(grid,0,i,m,n,vis);
            }
            if(vis[m-1][i]==false && grid[m-1][i]==0){
                dfs(grid,m-1,i,m,n,vis);
            }
        }
        for(int i=0;i<m;i++){
            if(vis[i][0]==false && grid[i][0]==0){
                dfs(grid,i,0,m,n,vis);
            }
            if(vis[i][n-1]==false && grid[i][n-1]==0){
                dfs(grid,i,n-1,m,n,vis);
            }
        }
        int count = 0;
        for(int i=0;i<m;i++){
            for(int j=0;j<n;j++){
                if(grid[i][j] == 0 && vis[i][j] == false){
                    dfs(grid,i,j,m,n,vis);
                    count++;
                }
            }
        }
        return count;
    }
};
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