Java Priority Queue - HackerRank Solution
Hello Friends, How are you? Today I will solve the HackerRank Java Priority Queue - Problem with a straightforward explanation. In this article, you will get more than one approach to solve this problem. So let's start-
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HackerRank Java Priority Queue - Problem Statement
In computer science, a priority queue is an abstract data type which is like a regular queue, but where additionally each element has a "priority" associated with it. In a priority queue, an element with high priority is served before an element with low priority. - Wikipedia
In this problem we will test your knowledge on Java Priority Queue.
There are a number of students in a school who wait to be served. Two types of events, ENTER and SERVED, can take place which are described below.
- ENTER: A student with some priority enters the queue to be served.
- SERVED: The student with the highest priority is served (removed) from the queue.
A unique id is assigned to each student entering the queue. The queue serves the students based on the following criteria (priority criteria):
- The student having the highest Cumulative Grade Point Average (CGPA) is served first.
- Any students having the same CGPA will be served by name in ascending case-sensitive alphabetical order.
- Any students having the same CGPA and name will be served in ascending order of the id.
Create the following two classes:
The Student class should implement:
- The constructor Student(int id, String name, double cgpa).
- The method int getID() to return the id of the student.
- The method String getName() to return the name of the student.
- The method double getCGPA() to return the CGPA of the student.
The Priorities class should implement the method List<Student> getStudents(List<String> events) to process all the given events and return all the students yet to be served in the priority order.
Input Format
The first line contains an integer, n, describing the total number of events. Each of the n subsequent lines will be of the following two forms:
- ENTER name CGPA id: The student to be inserted into the priority queue.
- SERVED: The highest priority student in the queue was served.
The locked stub code in the editor reads the input and tests the correctness of the Student and Priorities classes implementation.
Constraints:
- 2 <= n <= 1000
- 0 <= CGPA <= 4.00
- 1 <= id <= 10^5
- 2 <= |name| <= 30
Output Format
The locked stub code prints the names of the students yet to be served in the priority order. If there are no such student, then the code prints EMPTY.
Sample Input
12 ENTER John 3.75 50 ENTER Mark 3.8 24 ENTER Shafaet 3.7 35 SERVED SERVED ENTER Samiha 3.85 36 SERVED ENTER Ashley 3.9 42 ENTER Maria 3.6 46 ENTER Anik 3.95 49 ENTER Dan 3.95 50 SERVED {codeBox}
Sample Output
Dan Ashley Shafaet Maria {codeBox}
Explanation 0
In this case, the number of events is 12. Let the name of the queue be Q.
- John is added to Q. So, it contains (John, 3.75, 50).
- Mark is added to Q. So, it contains (John, 3.75, 50) and (Mark, 3.8, 24).
- Shafaet is added to Q. So, it contains (John, 3.75, 50), (Mark, 3.8, 24), and (Shafaet, 3.7, 35).
- Mark is served as he has the highest CGPA. So, Q contains (John, 3.75, 50) and (Shafaet, 3.7, 35).
- John is served next as he has the highest CGPA. So, Q contains (Shafaet, 3.7, 35).
- Samiha is added to Q. So, it contains (Shafaet, 3.7, 35) and (Samiha, 3.85, 36).
- Samiha is served as she has the highest CGPA. So, Q contains (Shafaet, 3.7, 35).
- Now, four more students are added to Q. So, it contains (Shafaet, 3.7, 35), (Ashley, 3.9, 42), (Maria, 3.6, 46), (Anik, 3.95, 49), and (Dan, 3.95, 50).
- Anik is served because though both Anil and Dan have the highest CGPA but Anik comes first when sorted in alphabetic order. So, Q contains (Dan, 3.95, 50), (Ashley, 3.9, 42), (Shafaet, 3.7, 35), and (Maria, 3.6, 46).
As all events are completed, the name of each of the remaining students is printed on a new line.
Java Priority Queue HackerRank Solution
Java Priority Queue - Hacker Rank Solution
Approach I: Java Priority Queue - Solution HackerRank
// ========================
// Information
// ========================
// Name: Java Priority Queue HackerRank Problem
// Direct Link: https://www.hackerrank.com/challenges/java-priority-queue/problem
// Difficulty: Medium
// Max Score: 20
// Language: Java 8
// ========================
// Solution Start
// ========================
// Java Priority Queue - Hacker Rank Solution Start
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
/*
* Create the Student and Priorities classes here.
*/
import java.util.Comparator;
import java.util.PriorityQueue;
class Student {
private final int id;
private final String name;
private final 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 {
private final PriorityQueue<Student> queue = new PriorityQueue<>(
Comparator.comparing(Student::getCGPA).reversed()
.thenComparing(Student::getName)
.thenComparing(Student::getID));
public List<Student> getStudents(List<String> events) {
events.forEach((event) -> {
if (event.equals("SERVED")) {
queue.poll();
} else {
String[] details = event.split(" ");
queue.add(new Student(Integer.parseInt(details[3]), details[1], Double.parseDouble(details[2])));
}
});
List<Student> students = new ArrayList<>();
while (!queue.isEmpty()) {
students.add(queue.poll());
}
return students;
}
}
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());
}
}
}
}
// Java Priority Queue Hacker Rank Solution END
// MyEduWavesApproach II: Java Priority Queue - Solution HackerRank
// ========================
// Information
// ========================
// Name: Java Priority Queue HackerRank Problem
// Direct Link: https://www.hackerrank.com/challenges/java-priority-queue/problem
// Difficulty: Medium
// Max Score: 20
// Language: Java 8
// ========================
// Solution Start
// ========================
// Java Priority Queue - Hacker Rank Solution Start
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
/*
* Create the Student and Priorities classes here.
*/
import java.util.PriorityQueue;
class Student implements Comparable<Student> {
int id;
String name;
double cgpa;
Student(int id, String name, double cgpa) {
this.id = id;
this.name = name;
this.cgpa = cgpa;
}
public int compareTo(Student b) {
if (this.cgpa > b.cgpa) { return -1; }
if (this.cgpa < b.cgpa) { return 1; }
if (this.cgpa == b.cgpa) {
if (this.name.compareTo(b.name) < 0 ) { return -1; }
if (this.name.compareTo(b.name) > 0) { return 1; }
if (this.name.compareTo(b.name) == 0) {
if (this.id < b.id) { return -1; }
if (this.id > b.id) { return 1; }
}
}
return 0;
}
public String getName() {
return name;
}
}
class Priorities {
Priorities() {}
public List<Student> getStudents(List<String> events) {
PriorityQueue<Student> queue = new PriorityQueue<Student>();
for (int i = 0; i < events.size(); i++) {
if (events.get(i).contains("SERVED")) {
if (queue.size() > 0) { queue.poll(); }
} else {
String[] data = events.get(i).split(" ");
queue.add(new Student(Integer.parseInt(data[3]), data[1], Double.valueOf(data[2])));
}
}
List<Student> result = new ArrayList<>();
while (queue.size() > 0) {
result.add(queue.poll());
}
return result;
}
}
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());
}
}
}
}
// Java Priority Queue Hacker Rank Solution END
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I hope you have understood the solution to this HackerRank Problem. All these three solutions will pass all the test cases. Now visit Java Priority Queue - Hackerrank Problem and try to solve it again.
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