<p>You are given a 2D array of axis-aligned <code>rectangles</code>. Each <code>rectangle[i] = [x<sub>i1</sub>, y<sub>i1</sub>, x<sub>i2</sub>, y<sub>i2</sub>]</code> denotes the <code>i<sup>th</sup></code> rectangle where <code>(x<sub>i1</sub>, y<sub>i1</sub>)</code> are the coordinates of the <strong>bottom-left corner</strong>, and <code>(x<sub>i2</sub>, y<sub>i2</sub>)</code> are the coordinates of the <strong>top-right corner</strong>.</p>

<p>Calculate the <strong>total area</strong> covered by all <code>rectangles</code> in the plane. Any area covered by two or more rectangles should only be counted <strong>once</strong>.</p>

<p>Return <em>the <strong>total area</strong></em>. Since the answer may be too large, return it <strong>modulo</strong> <code>10<sup>9</sup> + 7</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://s3-lc-upload.s3.amazonaws.com/uploads/2018/06/06/rectangle_area_ii_pic.png" style="width: 600px; height: 450px;" />
<pre>
<strong>Input:</strong> rectangles = [[0,0,2,2],[1,0,2,3],[1,0,3,1]]
<strong>Output:</strong> 6
<strong>Explanation:</strong> A total area of 6 is covered by all three rectangles, as illustrated in the picture.
From (1,1) to (2,2), the green and red rectangles overlap.
From (1,0) to (2,3), all three rectangles overlap.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> rectangles = [[0,0,1000000000,1000000000]]
<strong>Output:</strong> 49
<strong>Explanation:</strong> The answer is 10<sup>18</sup> modulo (10<sup>9</sup> + 7), which is 49.
</pre>

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

<ul>
	<li><code>1 &lt;= rectangles.length &lt;= 200</code></li>
	<li><code>rectanges[i].length == 4</code></li>
	<li><code>0 &lt;= x<sub>i1</sub>, y<sub>i1</sub>, x<sub>i2</sub>, y<sub>i2</sub> &lt;= 10<sup>9</sup></code></li>
	<li><code>x<sub>i1 &lt;= </sub>x<sub>i2</sub></code></li>
	<li><code>y<sub>i1 &lt;=</sub> y<sub>i2</sub></code></li>
</ul>

#include <vector>
#include <unordered_set>
#include <unordered_map>
#include <algorithm>
#include <iterator>

using std::vector;
using std::unordered_set;
using std::unordered_map;

class Solution
{
	public:
		int rectangleArea(vector<vector<int>>& rectangles)
		{
			unordered_set<int> uset {};
			vector<long long> xs {}, ys {};
			vector<vector<bool>> visited {};
			unordered_map<int, int> umapX {}, umapY {};
			long long total_area { 0LL };

			for(const auto& rectangle : rectangles)
			{
				uset.insert(rectangle[0]);
				uset.insert(rectangle[2]);
			}

			xs.reserve(uset.size());

			for(auto num : uset)
				xs.push_back(num);

			uset.clear();

			for(const auto& rectangle : rectangles)
			{
				uset.insert(rectangle[1]);
				uset.insert(rectangle[3]);
			}

			ys.reserve(uset.size());

			for(auto num : uset)
				ys.push_back(num);

			std::sort(xs.begin(), xs.end());
			std::sort(ys.begin(), ys.end());

			umapX.reserve(xs.size());
			umapY.reserve(ys.size());

			for(int i { 0 }; i < xs.size(); ++i)
				umapX.emplace(xs[i], i);

			for(int i { 0 }; i < ys.size(); ++i)
				umapY.emplace(ys[i], i);

			visited.reserve(xs.size() - 1);
			visited.assign(xs.size() - 1, vector<bool>(ys.size() - 1, false));

			for(const auto& rectangle : rectangles)
			{
				for(auto i { umapX.find(rectangle[0])->second }; xs[i] != rectangle[2]; ++i)
				{
					auto lenX { xs[i + 1] - xs[i] };

					for(auto j { umapY.find(rectangle[1])->second }; ys[j] != rectangle[3]; ++j)
					{
						if ( !visited[i][j] )
						{
							visited[i][j] = true;

							total_area += lenX * (ys[j + 1] - ys[j]);
						}
					}
				}
			}

			return static_cast<int>(total_area % mod);
		}

	private:
		const long long mod { 1000000007LL };
};

13600