MinimumHalls.java

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

class Lecture {
    int startTime;
    int endTime;

    public Lecture(int startTime, int endTime) {
        this.startTime = startTime;
        this.endTime = endTime;
    }
}

public class MinimumHalls {

    public static int minHalls(List<Lecture> lectures) {
        // Sort lectures based on start time
        Collections.sort(lectures, Comparator.comparingInt(l -> l.startTime));

        // List to keep track of allocated halls
        List<List<Lecture>> halls = new ArrayList<>();

        for (Lecture lecture : lectures) {
            boolean allocated = false;

            // Check each existing hall for availability
            for (List<Lecture> hall : halls) {
                if (lecture.startTime > hall.get(hall.size() - 1).endTime) {
                    // Assign lecture to existing hall
                    hall.add(lecture);
                    allocated = true;
                    break;
                }
            }

            if (!allocated) {
                // Create a new hall and assign lecture to it
                List<Lecture> newHall = new ArrayList<>();
                newHall.add(lecture);
                halls.add(newHall);
            }
        }

        // Number of halls used
        return halls.size();
    }

    public static void main(String[] args) {
        List<Lecture> lectures = new ArrayList<>();
        lectures.add(new Lecture(9, 10));
        lectures.add(new Lecture(10, 11));
        lectures.add(new Lecture(11, 12));
        lectures.add(new Lecture(9, 12));

        int minimumHalls = minHalls(lectures);
        System.out.println("Minimum number of halls required: " + minimumHalls);
    }
}