added java solution for Meeting Rooms II

java/253-Meeting-Rooms-ii.java

@@ -0,0 +1,34 @@
+/**
+ * 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
+     */
+    public int minMeetingRooms(List<Interval> intervals) {
+        if(intervals.isEmpty()) return 0;
+
+        Collections.sort(intervals, (a, b) -> Integer.compare(a.start, b.start));
+
+        Queue<Interval> queue = new PriorityQueue<>((a, b) -> Integer.compare(a.end, b.end));
+
+        int count = 0;
+        for (Interval interval : intervals) {
+
+            while(!queue.isEmpty() && interval.start >= queue.peek().end) queue.poll();
+
+            queue.offer(interval);
+            count = Math.max(count, queue.size());
+        }
+        return count;
+    }
+}