<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 i, int j, vector<vector<int>>& grid,
             vector<vector<int>>& visited, vector<int> row, vector<int> col,bool &flag) {
        if(i==0||j==0||i==grid.size()-1||j==grid[0].size()-1)
        flag=true;
        visited[i][j] = 1;

        for (int k = 0; k < 4; k++) {
            int n_r = i + row[k];
            int n_c = j + col[k];

            if (n_r >= 0 && n_c >= 0 && n_r < grid.size() &&
                n_c < grid[0].size() && grid[n_r][n_c] == 0 &&
                visited[n_r][n_c] == 0) {
                DFS(n_r, n_c, grid, visited, row, col,flag);
            }
        }
    }
    int closedIsland(vector<vector<int>>& grid) {
       
        int n = grid.size();
        int m = grid[0].size();
        vector<vector<int>> visited(n, vector<int>(m, 0));
        vector<int> row = {0, 0, 1, -1};
        vector<int> col = {1, -1, 0, 0};
        int cnt=0;
        for (int i = 1; i < n-1; i++) {
            for (int j = 1; j < m-1; j++) {
                if (grid[i][j] == 0 && visited[i][j] == 0) {
                    bool flag=false;
                    cnt++;
                    DFS(i, j, grid, visited, row, col,flag);
                    if(flag)
                    cnt--;
                }
            }
        }
        return cnt;
    }
};
16578