ActivitySelectionProblem.java

/*https://practice.geeksforgeeks.org/problems/n-meetings-in-one-room-1587115620/1/*/

class Solution 
{
    public static int maxMeetings(int start[], int end[], int n)
    {
        ArrayList<ArrayList<Integer>> list = new ArrayList<ArrayList<Integer>>();
        for (int i = 0; i < n; ++i)
        {
            ArrayList<Integer> temp = new ArrayList<Integer>();
            temp.add(start[i]);
            temp.add(end[i]);
            list.add(temp);
        }

        //sort according to the finish times
        Collections.sort(list,new Comparator<ArrayList<Integer>>()
        {
            public int compare(ArrayList<Integer> l1, ArrayList<Integer> l2)
            {
                return l1.get(1)-l2.get(1);
            }
        });

        //count
        int count = 0;
        int lastStart = -1, lastEnd = -1;
        for (ArrayList<Integer> duration : list)
        {
            //if the current meeting starts after the last meeting ends
            if (duration.get(0) > lastEnd)
            {
                //increment the count
                ++count;

                //update the last meeting
                lastStart = duration.get(0);
                lastEnd = duration.get(1);
            }
        }
        return count;
    }
}
/*Pratik's Solution*/

class Activity implements Comparable<Activity>
{
    int start;
    int end;
    Activity(int start,int end)
    {
        this.start = start;
        this.end = end;
    }
    public int compareTo(Activity a)
    {
        return this.end-a.end;
    }
}

class Solution 
{
    //Function to find the maximum number of meetings that can
    //be performed in a meeting room.
    
    public static int maxMeetings(int start[], int end[], int n)
    {
        // add your code here
        PriorityQueue<Activity> heap = new PriorityQueue<Activity>();
        for(int i=0;i<n;i++)
        {
            heap.add(new Activity(start[i],end[i]));
        }
        int k=0;
        while(!heap.isEmpty())
        {
            Activity cur = heap.poll();
            k++;
            while(!heap.isEmpty()&&heap.peek().start<=cur.end)heap.poll();
        }
        return k;
    }
}