Add meeting rooms2 solution

Author: sudheerj

src/java1/algorithms/interval/meetingRooms2.java

@@ -0,0 +1,70 @@
+package java1.algorithms.interval;
+import java.util.*;
+
+class Interval {
+    int start, end;
+    Interval(int start, int end) {
+        this.start = start;
+        this.end = end;
+    }
+}
+public class meetingRooms2 {
+    //Two pointer TC: O(n logn + n) SC: O(n)
+    private static int minMeetingRooms1(List<Interval> intervals) {
+        int length = intervals.size();
+        int[] startTimes = new int[length];
+        int[] endTimes = new int[length];
+        int minMeetingRooms = 0, count = 0;
+
+        for(int i=0; i<intervals.size(); i++) {
+            startTimes[i] = intervals.get(i).start;
+            endTimes[i] = intervals.get(i).end;
+        }
+        Arrays.sort(startTimes);
+        Arrays.sort(endTimes);
+
+        int startIndex =0, endIndex = 0;
+
+        while(startIndex < intervals.size()) {
+            if(startTimes[startIndex] < endTimes[endIndex]) {
+                count++;
+                startIndex++;
+            } else {
+                count--;
+                endIndex++;
+            }
+            minMeetingRooms = Math.max(minMeetingRooms, count);
+        }
+        return minMeetingRooms;
+    }
+
+    //Priority Queue + sorting:- TC: O(n logn + n) SC: O(n)
+    private static int minMeetingRooms2(List<Interval> intervals) {
+        Collections.sort(intervals, (a, b) -> a.start - b.start);
+        PriorityQueue<Interval> priorityQueue = new PriorityQueue<>((a, b) -> a.end-b.end);
+        priorityQueue.add(intervals.get(0));
+
+        for(int i=1; i< intervals.size(); i++) {
+            int endTime = priorityQueue.peek().end;
+            int startTime = intervals.get(i).start;
+            if(endTime <= startTime) {
+                priorityQueue.poll();
+            }
+            priorityQueue.add(intervals.get(i));
+        }
+
+        return priorityQueue.size();
+    }
+
+    public static void main(String[] args) {
+        List<Interval> intervals = new ArrayList<>();
+        intervals.add(new Interval(2, 7));
+        intervals.add(new Interval(3, 5));
+        intervals.add(new Interval(3, 9));
+        intervals.add(new Interval(5, 12));
+        intervals.add(new Interval(8, 15));
+        intervals.add(new Interval(9, 14));
+        System.out.println(minMeetingRooms1(intervals));
+        System.out.println(minMeetingRooms2(intervals));
+    }
+}

src/javascript/algorithms/interval/meetingRooms2.js

@@ -0,0 +1,34 @@
+//Two pointer TC: O(n logn + n) SC: O(n)
+
+function minMeetingRooms1(intervals) {
+    let startTimes = Array(intervals.length);
+    let endTimes = Array(intervals.length);
+
+    for(let [start, end] of intervals) {
+        startTimes.push(start);
+        endTimes.push(end);
+    }
+
+    startTimes.sort((a, b) => a-b);
+    endTimes.sort((a, b) => a-b);
+
+    let startTimeIndex = endTimeIndex = 0;
+    let minMeetingRooms = count = 0; 
+
+    while(startTimeIndex < intervals.length) {
+        let startTime = startTimes[startTimeIndex];
+        let endTime = endTimes[endTimeIndex];
+        if(startTime < endTime) {
+            startTimeIndex++;
+            count++;
+        } else {
+            endTimeIndex++;
+            count--;
+        }
+        minMeetingRooms = Math.max(minMeetingRooms, count);
+    }
+    return minMeetingRooms;
+}
+
+let intervals = [[2, 7], [3, 5], [3, 9], [5, 12], [8, 15], [9, 14]];
+console.log(minMeetingRooms1(intervals));