<p>You are given a <strong>0-indexed</strong> <code>m x n</code> binary matrix <code>land</code> where a <code>0</code> represents a hectare of forested land and a <code>1</code> represents a hectare of farmland.</p>

<p>To keep the land organized, there are designated rectangular areas of hectares that consist <strong>entirely</strong> of farmland. These rectangular areas are called <strong>groups</strong>. No two groups are adjacent, meaning farmland in one group is <strong>not</strong> four-directionally adjacent to another farmland in a different group.</p>

<p><code>land</code> can be represented by a coordinate system where the top left corner of <code>land</code> is <code>(0, 0)</code> and the bottom right corner of <code>land</code> is <code>(m-1, n-1)</code>. Find the coordinates of the top left and bottom right corner of each <strong>group</strong> of farmland. A <strong>group</strong> of farmland with a top left corner at <code>(r<sub>1</sub>, c<sub>1</sub>)</code> and a bottom right corner at <code>(r<sub>2</sub>, c<sub>2</sub>)</code> is represented by the 4-length array <code>[r<sub>1</sub>, c<sub>1</sub>, r<sub>2</sub>, c<sub>2</sub>].</code></p>

<p>Return <em>a 2D array containing the 4-length arrays described above for each <strong>group</strong> of farmland in </em><code>land</code><em>. If there are no groups of farmland, return an empty array. You may return the answer in <strong>any order</strong></em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/07/27/screenshot-2021-07-27-at-12-23-15-copy-of-diagram-drawio-diagrams-net.png" style="width: 300px; height: 300px;" />
<pre>
<strong>Input:</strong> land = [[1,0,0],[0,1,1],[0,1,1]]
<strong>Output:</strong> [[0,0,0,0],[1,1,2,2]]
<strong>Explanation:</strong>
The first group has a top left corner at land[0][0] and a bottom right corner at land[0][0].
The second group has a top left corner at land[1][1] and a bottom right corner at land[2][2].
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/07/27/screenshot-2021-07-27-at-12-30-26-copy-of-diagram-drawio-diagrams-net.png" style="width: 200px; height: 200px;" />
<pre>
<strong>Input:</strong> land = [[1,1],[1,1]]
<strong>Output:</strong> [[0,0,1,1]]
<strong>Explanation:</strong>
The first group has a top left corner at land[0][0] and a bottom right corner at land[1][1].
</pre>

<p><strong class="example">Example 3:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/07/27/screenshot-2021-07-27-at-12-32-24-copy-of-diagram-drawio-diagrams-net.png" style="width: 100px; height: 100px;" />
<pre>
<strong>Input:</strong> land = [[0]]
<strong>Output:</strong> []
<strong>Explanation:</strong>
There are no groups of farmland.
</pre>

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

<ul>
	<li><code>m == land.length</code></li>
	<li><code>n == land[i].length</code></li>
	<li><code>1 &lt;= m, n &lt;= 300</code></li>
	<li><code>land</code> consists of only <code>0</code>&#39;s and <code>1</code>&#39;s.</li>
	<li>Groups of farmland are <strong>rectangular</strong> in shape.</li>
</ul>

#define FORESTLAND              0
#define FARMLAND                1
#define DISCOVERED_FARMLAND     2

class Solution {
public:

    /* =========================================================
     *
     * plot_farmland():
     *
     * Use BFS to map out entire group of farmland starting from
     * the origin point, which is the top-leftmost position of 
     * that group. 
     *
     * ========================================================= */
    void plot_farmland(vector<vector<int>>& land, vector<vector<int>>& farmland_coords, int x, int y, int m, int n) {

        vector<int> farmland_corners;
        farmland_corners.push_back(x);
        farmland_corners.push_back(y);
        int curr_x = x, curr_y = y;

        queue<pair<int,int>> queue;
        queue.push(make_pair(x,y));

        while (!queue.empty()) {

            auto coords = queue.front();
            curr_x = coords.first;
            curr_y = coords.second;
            queue.pop();

            /* Queue in-bounds neighbors to the right and bottom if they are undiscovered farmland */
            if (curr_x + 1 < m && (land[curr_x + 1][curr_y] != FORESTLAND && land[curr_x + 1][curr_y] != DISCOVERED_FARMLAND)) { queue.push(make_pair(curr_x + 1, curr_y)); land[curr_x + 1][curr_y] = DISCOVERED_FARMLAND;; }
            if (curr_y + 1 < n && (land[curr_x][curr_y + 1] != FORESTLAND && land[curr_x][curr_y + 1] != DISCOVERED_FARMLAND)) { queue.push(make_pair(curr_x, curr_y + 1)); land[curr_x][curr_y + 1] = DISCOVERED_FARMLAND;; }
        }

        farmland_corners.push_back(curr_x);
        farmland_corners.push_back(curr_y);
        farmland_coords.push_back(farmland_corners);
    }

    /* =========================================================
     *
     * findFarmland():
     *
     * ========================================================= */
    vector<vector<int>> findFarmland(vector<vector<int>>& land) {

        int m = land.size();
        int n = land[0].size();
        vector<vector<int>> farmland_coords;

        /* Scan the matrix and run BFS when farmland is discovered */
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (land[i][j] == FARMLAND) {
                    plot_farmland(land, farmland_coords, i, j, m, n);
                }
            }
        }

        return farmland_coords;
    }
};
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