<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 bfs(int x, int y, int numRows, int numCols, vector<vector<int>>& grid, vector<vector<bool>> &visited) {
        queue<pair<int, int>> bfsQueue;
        bfsQueue.push({x, y});
        visited[x][y] = true;
        bool isClosed = true;
        vector<pair<int, int>> directions = {{1, 0}, {0, 1}, {-1, 0}, {0, -1}};

        while (!bfsQueue.empty()) {
            x = bfsQueue.front().first;
            y = bfsQueue.front().second;
            bfsQueue.pop();

            for (auto direction: directions) {
                int x2 = x + direction.first;
                int y2 = y + direction.second;
                if (!(x2 >= 0 && y2 >= 0 && x2 < numRows && y2 < numCols)) {
                    isClosed = false;
                }
                else if (grid[x2][y2] == 0 && !visited[x2][y2]) {
                    bfsQueue.push({x2, y2});
                    visited[x2][y2] = true;
                }
            }
        }
        return isClosed;
    }
    int closedIsland(vector<vector<int>>& grid) {
        int numRows = grid.size();
        int numCols = grid[0].size();

        int numOfClosedIslands = 0;

        vector<vector<bool>> visited(numRows, vector<bool>(numCols, false));

        for (int row = 0; row < numRows; row++) {
            for (int col = 0; col <numCols; col++) {
                if (grid[row][col] == 0 && !visited[row][col] && bfs(row, col, numRows, numCols, grid, visited)) {
                    numOfClosedIslands++;
                }
            }
        }
        return numOfClosedIslands;
    }
};
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