@@ -562,6 +562,7 @@
 | [845. Longest Mountain in Array](https://leetcode.com/problems/longest-mountain-in-array/) | [Solution](https://.com/fluency03/leetcode-java/blob/master/src/LongestMountainInArray845.java) | Medium |
 | [846. Hand of Straights](https://leetcode.com/problems/hand-of-straights/) | [Solution](https://.com/fluency03/leetcode-java/blob/master/src/HandOfStraights846.java) | Medium |
 | [849. Maximize Distance to Closest Person](https://leetcode.com/problems/maximize-distance-to-closest-person/) | [Solution](https://.com/fluency03/leetcode-java/blob/master/src/MaximizeDistanceToClosestPerson849.java) | Easy |
+| [850. Rectangle Area II](https://leetcode.com/problems/rectangle-area-ii/) | [Solution](https://.com/fluency03/leetcode-java/blob/master/src/RectangleAreaII850.java) | Hard |
 | [855. Exam Room](https://leetcode.com/problems/exam-room/) | [Solution](https://.com/fluency03/leetcode-java/blob/master/src/ExamRoom855.java) | Medium |
 | [859. Buddy Strings](https://leetcode.com/problems/buddy-strings/) | [Solution](https://.com/fluency03/leetcode-java/blob/master/src/BuddyStrings859.java) | Easy |
 | [860. Lemonade Change](https://leetcode.com/problems/lemonade-change/) | [Solution](https://.com/fluency03/leetcode-java/blob/master/src/LemonadeChange860.java) | Easy |

@@ -0,0 +1,81 @@
+/**
+* We are given a list of (axis-aligned) rectangles. Each rectangle[i] =
+* [x1, y1, x2, y2] , where (x1, y1) are the coordinates of the bottom-left
+* corner, and (x2, y2) are the coordinates of the top-right corner of the ith
+* rectangle.
+*
+* Find the total area covered by all rectangles in the plane. Since the
+* answer may be too large, return it modulo 10^9 + 7.
+*
+* https://s3-lc-upload.s3.amazonaws.com/uploads/2018/06/06/rectangle_area_ii_pic.png
+*
+* Example 1:
+* Input: [[0,0,2,2],[1,0,2,3],[1,0,3,1]]
+* Output: 6
+* Explanation: As illustrated in the picture.
+*
+* Example 2:
+* Input: [[0,0,1000000000,1000000000]]
+* Output: 49
+* Explanation: The answer is 10^18 modulo (10^9 + 7), which is (10^9)^2 = (-7)^2 = 49.
+*
+* Note:
+* 1 <= rectangles.length <= 200
+* rectanges[i].length = 4
+* 0 <= rectangles[i][j] <= 10^9
+* The total area covered by all rectangles will never exceed 2^63 - 1 and
+* thus will fit in a 64-bit signed integer.
+*/
+
+
+public class RectangleAreaII850 {
+/**
+* https://leetcode.com/problems/rectangle-area-ii/
+*/
+public int rectangleArea(int[][] rectangles) {
+int OPEN = 0, CLOSE = 1;
+int[][] events = new int[rectangles.length * 2][];
+int t = 0;
+for (int[] rec: rectangles) {
+events[t++] = new int[]{rec[1], OPEN, rec[0], rec[2]};
+events[t++] = new int[]{rec[3], CLOSE, rec[0], rec[2]};
+}
+
+Arrays.sort(events, (a, b) -> Integer.compare(a[0], b[0]));
+
+List<int[]> active = new ArrayList();
+int cur_y = events[0][0];
+long ans = 0;
+for (int[] event: events) {
+int y = event[0], typ = event[1], x1 = event[2], x2 = event[3];
+
+// Calculate query
+long query = 0;
+int cur = -1;
+for (int[] xs: active) {
+cur = Math.max(cur, xs[0]);
+query += Math.max(xs[1] - cur, 0);
+cur = Math.max(cur, xs[1]);
+}
+
+ans += query * (y - cur_y);
+
+if (typ == OPEN) {
+active.add(new int[]{x1, x2});
+Collections.sort(active, (a, b) -> Integer.compare(a[0], b[0]));
+} else {
+for (int i = 0; i < active.size(); ++i)
+if (active.get(i)[0] == x1 && active.get(i)[1] == x2) {
+active.remove(i);
+break;
+}
+}
+
+cur_y = y;
+}
+
+ans %= 1_000_000_007;
+return (int) ans;
+}
+
+}