<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 numislands(vector<vector<int>> grid) {
        vector<pair<int, int>> d = {{1, 0}, {0, 1}, {-1, 0}, {0, -1}};
        int m = grid.size(), n = grid[0].size();
        int res =0;
        queue<pair<int, int>> q;

        for (int i = 0; i < m; ++i) {
            for (int j = 0; j < n; ++j) {
                if (grid[i][j] == 1) {
                    res += 1;
                    q.push({i, j});

                    while (!q.empty()) {
                        auto [x, y] = q.front();
                        q.pop();
                        if (x < 0 or x >= m or y < 0 or y >= n or
                            grid[x][y] != 1)
                            continue;

                        grid[x][y] = 0;

                        for (auto& dir : d) {
                            int nx = x + dir.first;
                            int ny = y + dir.second;
                            if (nx >= 0 and nx < m and ny >= 0 and ny < n and
                                grid[nx][ny] == 1)
                                q.push({nx, ny});
                        }
                    }
                }
            }
        }
        return res;
    }


    int minDays(vector<vector<int>>& grid) {
        int num = numislands(grid);
        if(num!=1)
        return 0;

        for(int i =0;i<grid.size();++i)
        {
            for(int j =0;j<grid[i].size();++j)
            {
                if(grid[i][j]==1)
                {
                    grid[i][j]=0;
                    if(numislands(grid)!=1)
                    return 1;

                    grid[i][j]=1;
                }
            }
        }
        return 2;
    }
};
53020