<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 numLand(vector<vector<int>>& grid) {
        static const array<pair<int, int>, 4> direction{{{-1, 0}, {1, 0}, {0, -1}, {0, 1}}};
        const int n = grid.size(), m = grid[0].size();
        int ans = 0;
        vector<vector<bool> > isReach(n, vector<bool>(m, false));

        queue<pair<int, int> > q;
        int starti = 0, startj = 0;
        while (starti < n && startj < m && grid[starti][startj] == 0) {
            starti += (++startj) / m;
            startj %= m;
        }
        if (starti >= n) {
            return 0;
        }
        q.push(make_pair(starti, startj));
        isReach[starti][startj] = true;
        while (!q.empty()) {
            auto [i, j] = q.front();
            q.pop();
            for (auto [di, dj] : direction) {
                const int x = i + di, y = j + dj;
                if (x >= 0 && x < n && y >= 0 && y < m && !isReach[x][y] && grid[x][y] == 1) {
                    q.push(make_pair(x, y));
                    isReach[x][y] = true;
                }
            }
        }
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                if (grid[i][j] == 1 && !isReach[i][j]) {
                    return 2;
                }
            }
        }

        return 1;
    }

    int minDays(vector<vector<int>>& grid) {
        int num = numLand(grid);
        if (num == 0 || num > 1) {
            return 0;
        }
        for (int i = 0; i < grid.size(); i++) {
            for (int j = 0; j < grid[0].size(); j++) {
                if (grid[i][j] == 1) {
                    grid[i][j] = 0;
                    num = numLand(grid);
                    if (num == 0 || num > 1) {
                        return 1;
                    }
                    grid[i][j] = 1;
                }
            }
        }
        return 2;
    }
};
36780