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  1. Prepare
  2. Java
  3. Data Structures
  4. Java Priority Queue
  5. Discussions

Java Priority Queue

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  • vishva31072005
     + 0 comments

    class Student { private int id; private String name; private double cgpa;

    public Student(int id, String name, double cgpa) {
    this.id = id;
    this.name = name;
    this.cgpa = cgpa;
}

public int getID() { return id; }
public String getName() { return name; }
public double getCGPA() { return cgpa; }

    }

    class Priorities { public List getStudents(List events) {

        PriorityQueue<Student> queue = new PriorityQueue<>(new Comparator<Student>() {
        public int compare(Student s1, Student s2) {
            if (s1.getCGPA() != s2.getCGPA())
                return Double.compare(s2.getCGPA(), s1.getCGPA());
            else if (!s1.getName().equals(s2.getName()))
                return s1.getName().compareTo(s2.getName());
            else
                return s1.getID() - s2.getID();
        }
    });

    for (String event : events) {
        String[] parts = event.split(" ");

        if (parts[0].equals("ENTER")) {
            queue.add(new Student(
                Integer.parseInt(parts[3]),
                parts[1],
                Double.parseDouble(parts[2])
            ));
        } else if (parts[0].equals("SERVED")) {
            if (!queue.isEmpty())
                queue.poll();
        }
    }

    List<Student> students = new ArrayList<>();
    while (!queue.isEmpty()) {
        students.add(queue.poll());
    }

    return students;
}

  • vishva31072005
     + 0 comments

    class Student { private int id; private String name; private double cgpa;

    public Student(int id, String name, double cgpa) {
    this.id = id;
    this.name = name;
    this.cgpa = cgpa;
}

public int getID() { return id; }
public String getName() { return name; }
public double getCGPA() { return cgpa; }

    }

    class Priorities { public List getStudents(List events) {

        PriorityQueue<Student> queue = new PriorityQueue<>(new Comparator<Student>() {
        public int compare(Student s1, Student s2) {
            if (s1.getCGPA() != s2.getCGPA())
                return Double.compare(s2.getCGPA(), s1.getCGPA());
            else if (!s1.getName().equals(s2.getName()))
                return s1.getName().compareTo(s2.getName());
            else
                return s1.getID() - s2.getID();
        }
    });

    for (String event : events) {
        String[] parts = event.split(" ");

        if (parts[0].equals("ENTER")) {
            queue.add(new Student(
                Integer.parseInt(parts[3]),
                parts[1],
                Double.parseDouble(parts[2])
            ));
        } else if (parts[0].equals("SERVED")) {
            if (!queue.isEmpty())
                queue.poll();
        }
    }

    List<Student> students = new ArrayList<>();
    while (!queue.isEmpty()) {
        students.add(queue.poll());
    }

correct output for this program 

    return students;
}

    }

  • agonzalezcharrie
     + 0 comments
    import java.util.PriorityQueue;
import java.util.Comparator;

class Student {
    private int id;
    private String name;
    private double cgpa;
    
    public int getId(){return this.id;}
    public String getName(){return this.name;}
    public double getCGPA(){ return this.cgpa;}
    
    public Student(String id, String name, String cgpa){
        this.id = Integer.parseInt(id);
        this.name = name;
        this.cgpa = Double.parseDouble(cgpa);
    }
 }
 
class Priorities {
    // No attributes required
    public List<Student> getStudents(List<String> events){
        List<Student> out = new ArrayList<>();
        PriorityQueue<Student> pq = new PriorityQueue<Student>(
            Comparator.comparing(Student::getCGPA, Comparator.reverseOrder())
            .thenComparing(Student::getName)
            .thenComparing(Student::getId));

        // O(n log k)
        events.forEach(eventString -> 
        {
            String[] parts = eventString.split(" ");
            if("SERVED".equals(parts[0])){
                pq.poll();
            }else{
                Student student = new Student(parts[3], parts[1], parts[2]);
                pq.add(student);
            }
        });
        
        // O(m log m)
        while(!pq.isEmpty()){
            out.add(pq.poll());
        }
        
        // Overall complexity: O(n log k) when k < n,
        // worst scenario O(n log n) when n = k
        return out;
    }
 }

  • HelenFleischer5
     + 0 comments

    Nice problem — it really checks whether you understand how ordering works inside a priority queue rather than just using it blindly. Telugu 365 ID Login

  • deepak2322005
     + 0 comments

    import java.util.ArrayList; import java.util.List; import java.util.Scanner;

    import java.util.Comparator; import java.util.PriorityQueue; import java.util.Scanner; import java.util.*; class Student implements Comparable{ String name = new String(); double cgpa; int id; public Student(String name, double cgpa,int id){ this.name = name; this.cgpa =cgpa; this.id = id; } public String getName(){ return this.name; } public int compareTo(Student s) { if(cgpa == s.cgpa) { if(name.compareTo(s.name) == 0) { if(id == s.id) return 0; else if (id > s.id) return 1; else return -1; } else return name.compareTo(s.name); } else if(cgpa > s.cgpa) return -1; else return 1; } }

    class Priorities{ public ArrayList getStudents(List events) { int n = events.size(); PriorityQueue pq = new PriorityQueue(); for(String i:events) { String[] s = new String[4]; s = i.split("\s+"); if(s.length>1) { pq.add(new Student(s[1],Double.valueOf(s[2]),Integer.valueOf(s[3]))); } else { pq.poll(); } } while(pq.size()>1) { System.out.println(pq.poll().name); } return new ArrayList(pq); } }

    public class Solution { private final static Scanner scan = new Scanner(System.in); private final static Priorities priorities = new Priorities();

    public static void main(String[] args) {
    int totalEvents = Integer.parseInt(scan.nextLine());    
    List<String> events = new ArrayList<>();

    while (totalEvents-- != 0) {
        String event = scan.nextLine();
        events.add(event);
    }

    List<Student> students = priorities.getStudents(events);

    if (students.isEmpty()) {
        System.out.println("EMPTY");
    } else {
        for (Student st: students) {
            System.out.println(st.getName());
        }
    }
}

    }