<p>You are given an <code>m x n</code> binary grid <code>grid</code> where <code>1</code> represents land and <code>0</code> represents water. An <strong>island</strong> is a maximal <strong>4-directionally</strong> (horizontal or vertical) connected group of <code>1</code>&#39;s.</p>

<p>The grid is said to be <strong>connected</strong> if we have <strong>exactly one island</strong>, otherwise is said <strong>disconnected</strong>.</p>

<p>In one day, we are allowed to change <strong>any </strong>single land cell <code>(1)</code> into a water cell <code>(0)</code>.</p>

<p>Return <em>the minimum number of days to disconnect the grid</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/12/24/land1.jpg" style="width: 500px; height: 169px;" />
<pre>
<strong>Input:</strong> grid = [[0,1,1,0],[0,1,1,0],[0,0,0,0]]

<strong>Output:</strong> 2
<strong>Explanation:</strong> We need at least 2 days to get a disconnected grid.
Change land grid[1][1] and grid[0][2] to water and get 2 disconnected island.
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/12/24/land2.jpg" style="width: 404px; height: 85px;" />
<pre>
<strong>Input:</strong> grid = [[1,1]]
<strong>Output:</strong> 2
<strong>Explanation:</strong> Grid of full water is also disconnected ([[1,1]] -&gt; [[0,0]]), 0 islands.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>m == grid.length</code></li>
	<li><code>n == grid[i].length</code></li>
	<li><code>1 &lt;= m, n &lt;= 30</code></li>
	<li><code>grid[i][j]</code> is either <code>0</code> or <code>1</code>.</li>
</ul>

class Solution {
public:
    int num_of_islands(vector<vector<int>> &grid)
    {
        int n = grid.size(); 
        int m = grid[0].size();

        vector<vector<int>> vis(n, vector<int>(m, 0));
        int ans = 0;
        
        for(int i = 0; i<n; i++)
        {
            for(int j = 0; j<m; j++)
            {
                if(!vis[i][j] && grid[i][j])
                {
                    ans++;
                    queue<pair<int, int>> q;
                    q.push({i, j});
                    vis[i][j] = 1;
                    while(!q.empty())
                    {
                        int x = q.front().first;
                        int y = q.front().second;
                        q.pop();

                        //left
                        if(y-1 >= 0 && grid[x][y-1] && !vis[x][y-1])
                        {
                            vis[x][y-1] = 1;
                            q.push({x, y-1});
                        }

                        //right
                        if(y+1 < m && grid[x][y+1] && !vis[x][y+1])
                        {
                            vis[x][y+1] = 1;
                            q.push({x, y+1});
                        }

                        //up
                        if(x-1 >= 0 && grid[x-1][y] && !vis[x-1][y])
                        {
                            vis[x-1][y] = 1;
                            q.push({x-1, y});
                        }

                        //down
                        if(x+1 < n && grid[x+1][y] && !vis[x+1][y])
                        {
                            vis[x+1][y] = 1;
                            q.push({x+1, y});
                        }
                    }
                }
            }
        }
        return ans;
    }


    int minDays(vector<vector<int>>& grid) {
        int n = grid.size();
        int m = grid[0].size();

        if(num_of_islands(grid) != 1)
            return 0;
            
        for(int i = 0; i<n; i++)
        {
            for(int j = 0; j<m; j++)
            {
                if(grid[i][j])
                {
                    grid[i][j] = 0;
                    if(num_of_islands(grid) != 1)
                    {
                        return 1;
                    }
                    grid[i][j] = 1;
                }
            }
        }

        return 2;
    }
};
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