Solution for "Meeting Rooms II"

Author: Thuy Trinh

build.gradle

@@ -1,5 +1,5 @@
 buildscript {
-  ext.kotlinVersion = '1.1.51'
+  ext.kotlinVersion = '1.1.60'
 
   repositories {
     mavenCentral()

src/main/java/leetcode/meetingrooms2/README.md

@@ -0,0 +1,25 @@
+i0: [1,5]
+i1: [2,3]
+i3: [3,5]
+i4: [7,8]
+
+Given a list of rooms, and a given event, 
+which room we should add to achieve min count of rooms? 
+Choose the room having earliest finish. However, if the event overlaps with the 
+room, that means it can't fit the other rooms. So, new room should be created.
+
+If we have a list of events, which event we should choose to achieve min count 
+of rooms? With a room having earliest finish, the gap between room finish time 
+and the event's start time should be minimal. That means, we should select the 
+event having earliest start time.
+
+Solution:
+
+* Sort by earliest start
+* For each event and given a room list:
+  * Select a room having earliest finish
+  * If we can't add this event into the selected room, 
+  that means we can't add it into other rooms. 
+  So create a new room for this event.
+  * Otherwise, add it into the selected room. 
+  Also, we'll have to change the finish time of this room.

src/main/java/leetcode/meetingrooms2/Solution.kt

@@ -0,0 +1,33 @@
+package leetcode.meetingrooms2
+
+import leetcode.meetingrooms.Interval
+import java.util.*
+
+typealias RoomEndTime = Int
+typealias Rooms = PriorityQueue<RoomEndTime>
+
+/**
+ * https://leetcode.com/problems/meeting-rooms-ii/description/
+ */
+class Solution {
+  private fun RoomEndTime.hasNoOverlap(i: Interval): Boolean = this <= i.start
+
+  fun minMeetingRooms(intervals: Array<Interval>): Int {
+    if (intervals.isEmpty()) {
+      return 0
+    }
+
+    intervals.sortBy { it.start }
+    val rooms = Rooms()
+    intervals.forEach {
+      when {
+        rooms.isNotEmpty() && rooms.peek().hasNoOverlap(it) -> {
+          rooms.poll()
+          rooms.offer(it.end)
+        }
+        else -> rooms.offer(it.end)
+      }
+    }
+    return rooms.size
+  }
+}

src/test/java/leetcode/meetingrooms2/SolutionTest.kt

@@ -0,0 +1,24 @@
+package leetcode.meetingrooms2
+
+import leetcode.meetingrooms.Interval
+import org.amshove.kluent.shouldEqualTo
+import org.junit.Test
+
+class SolutionTest {
+  @Test
+  fun test() {
+    Solution().minMeetingRooms(arrayOf(
+        Interval(1, 5),
+        Interval(2, 3),
+        Interval(3, 5),
+        Interval(7, 8)
+    )).shouldEqualTo(2)
+    Solution().minMeetingRooms(arrayOf(
+        Interval(2, 15),
+        Interval(36, 45),
+        Interval(9, 29),
+        Interval(16, 23),
+        Interval(4, 9)
+    )).shouldEqualTo(2)
+  }
+}