<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:
    int dirx[4] = {0, 0, -1, 1};
    int diry[4] = {1, -1, 0, 0};
    int closedIsland(vector<vector<int>>& grid) {

        int n = grid.size(), m = grid[0].size();
        int count = 0;
        vector<vector<int>> vis(n, vector<int>(m, 0));

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

        unordered_set<int> notClosed, closed;

        for (int i = 0; i < m; i++) {
            if (vis[0][i] != 0) notClosed.insert(vis[0][i]);
            if (vis[n - 1][i] != 0) notClosed.insert(vis[n - 1][i]);
        }

        for (int i = 0; i < n; i++) {
            if (vis[i][0] != 0) notClosed.insert(vis[i][0]);
            if (vis[i][m - 1] != 0) notClosed.insert(vis[i][m - 1]);
        }

        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                if (vis[i][j] != 0 && notClosed.find(vis[i][j]) == notClosed.end()) {
                    closed.insert(vis[i][j]);
                }
            }
        }

        return closed.size();
    }

    void dfs(int x, int y, int count, vector<vector<int>>& grid, vector<vector<int>>& vis) {
        vis[x][y] = count;

        for (int i = 0; i < 4; i++) {
            int x1 = x + dirx[i];
            int y1 = y + diry[i];

            if (isValid(x1, y1, grid.size(), grid[0].size()) && grid[x1][y1] == 0 && vis[x1][y1] == 0) {
                dfs(x1, y1, count, grid, vis);
            }
        }
    }

    bool isValid(int x, int y, int n, int m) {
        if (x < 0 || x >= n || y < 0 || y >= m) {
            return 0;
        }
        return 1;
    }
};
14319