add meeting rooms 2 solution

Author: Tessa1217

meeting-rooms-ii/Tessa1217.java

@@ -0,0 +1,55 @@
+import java.util.List;
+import java.util.PriorityQueue;
+
+/**
+ * Definition of Interval:
+ * public class Interval {
+ *     int start, end;
+ *     Interval(int start, int end) {
+ *         this.start = start;
+ *         this.end = end;
+ *     }
+ * }
+ */
+
+public class Solution {
+    /**
+     * @param intervals: an array of meeting time intervals
+     * @return: the minimum number of conference rooms required
+     */
+    // 시간복잡도: O(n log n)
+    public int minMeetingRooms(List<Interval> intervals) {
+
+        if (intervals == null || intervals.isEmpty()) {
+            return 0;
+        }
+
+        // 주어진 시간 인터벌 리스트를 시작 시간 기준으로 정렬
+        intervals.sort((i1, i2) -> i1.start - i2.start);
+
+        // PriorityQueue 선언: 시간 interval의 end time 기준
+        PriorityQueue<Interval> meetingRooms = new PriorityQueue<>((i1, i2) -> i1.end - i2.end);
+
+        for (Interval interval : intervals) {
+
+            // 최초 meeting room 
+            if (meetingRooms.isEmpty()) {
+                meetingRooms.offer(interval);
+                continue;
+            }
+
+            Interval meeting = meetingRooms.peek();
+            // (0, 8), (8, 10) is not conflict at 8
+            if (meeting.end <= interval.start) {
+                // 앞의 회의 종료되었으므로 회의실 재사용
+                meetingRooms.poll();
+            }
+            // 새 회의실 추가
+            meetingRooms.offer(interval);
+        }
+
+        return meetingRooms.size();
+
+    }
+}
+