<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<pair<int,int>> dir = {{0,1}, {1,0}, {0,-1}, {-1,0}};
    int n,m;
    void dfs(int x, int y, vector<vector<int>>& grid, vector<vector<int>>&vis){
        vis[x][y] = 1;
        for(auto [dx,dy] : dir){
            int nx = x + dx;
            int ny = y + dy;
            if(nx >= 0 && nx < n && ny >= 0 && ny < m && grid[nx][ny] == 0 && !vis[nx][ny]){
                dfs(nx,ny,grid,vis);
            }
        }
    }
    int closedIsland(vector<vector<int>>& grid) {
        n = grid.size(), m = grid[0].size();
        vector<vector<int>>vis(n,vector<int>(m,0));
        for(int i = 0; i < n; i++){
            if(!vis[i][0] && grid[i][0] == 0) dfs(i,0,grid,vis);
            if(!vis[i][m-1] && grid[i][m-1] == 0) dfs(i,m-1,grid,vis);
        }
        for(int j = 0; j < m; j++){
            if(!vis[0][j] && grid[0][j] == 0) dfs(0,j,grid,vis);
            if(!vis[n-1][j] && grid[n-1][j] == 0) dfs(n-1,j,grid,vis);
        }
        int ans = 0;
        for(int i = 0; i < n; i++){
            for(int j = 0; j < m; j++){
                if(!vis[i][j] && grid[i][j] == 0){
                    dfs(i,j,grid,vis);
                    ans++;
                }
            }
        }
        return ans;
    }
};
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