Added 25 solutions

Java/Data Structures/Java Priority Queue/Solution.java

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+//     Author: Rodney Shaghoulian
+//     Github: github.com/rshaghoulian
+// HackerRank: hackerrank.com/rshaghoulian
+
+import java.util.Scanner;
+import java.util.PriorityQueue;
+import java.util.Comparator;
+
+class Student{
+    private String fname;
+    private double cgpa;
+    private int token;
+    public Student(String fname, double cgpa, int token) {
+        this.fname = fname;
+        this.cgpa = cgpa;
+        this.token = token;
+    }
+    public int getToken() {
+        return token;
+    }
+    public String getFname() {
+        return fname;
+    }
+    public double getCgpa() {
+        return cgpa;
+    }
+}
+
+public class Solution {
+    public static void main(String[] args) {
+        Scanner scan = new Scanner(System.in);
+        int n = scan.nextInt();
+        
+        /* Create PriorityQueue and add/remove entries */
+        PriorityQueue<Student> pq = new PriorityQueue<>(n, new StudentComparator());
+        while (n-- > 0) {
+            String event = scan.next();
+            switch (event) {
+                case "ENTER":
+                    String fname = scan.next();
+                    double cgpa  = scan.nextDouble();
+                    int    token = scan.nextInt();
+                    pq.add(new Student(fname, cgpa, token));
+                    break;
+                case "SERVED":
+                    pq.poll();
+                    break;
+                default:
+                    break;
+            } 
+        }
+        scan.close();
+        
+        /* Print Student names */
+        if (pq.isEmpty()) {
+            System.out.println("EMPTY");
+        } else {
+            while ( ! pq.isEmpty()) {
+                Student s = pq.remove();
+                System.out.println(s.getFname());
+            }
+        }
+    }
+}
+
+class StudentComparator implements Comparator<Student> {
+    double epsilon = 0.001; // since we shouldn't use "==" with doubles
+    @Override
+    public int compare(Student s1, Student s2) {
+        if (Math.abs(s1.getCgpa() - s2.getCgpa()) > epsilon) {
+            return s1.getCgpa() < s2.getCgpa() ? 1 : -1; // descending order
+        } else if ( ! s1.getFname().equals(s2.getFname())) {
+            return s1.getFname().compareTo(s2.getFname());
+        } else {
+            return s1.getToken() - s2.getToken();
+        }
+    }
+}