Question

Java program

The round-robin scheduling problem: using queue

There are n processes in a queue. Each process has name_i and time_i. The round-robin scheduling handles the processes in order. A round-robin scheduler gives each process a quantum (a time slot) and interrupts the process if it is not completed by then. The process is resumed and moved to the end of the queue, then the scheduler handles the next process in the queue.

For example, we have the following queue with the quantum of 100ms.

A(150) - B(80) - C(200) - D(200)

First, process A is handled for 100ms, then the process is moved to the end of the queue with the remaining time (50ms).

B(80) - C(200) - D(200) - A(50)

Next, process B is handled for 80ms. The process is completed with the time stamp of 180ms and removed from the queue.

C(200) - D(200) - A(50)

Your task is to write a program which simulates the round-robin scheduling.

Input:

n q
name₁ time₁
name₂ time₂
...
name_n time_n

In the first line the number of processes n and the quantum q are given separated by a single space.

In the following n lines, names and times for the n processes are given. name_i and time_i are separated by a single space.

Output: For each process, prints its name and the time the process finished in order.

Constraints:

• 1 ≤ n ≤ 100000
• 1 ≤ q ≤ 1000
• 1 ≤ time_i ≤ 50000
• 1 ≤ length of name_i ≤ 10
• 1 ≤ Sum of time_i ≤ 1000000

Sample Input 1

5 100
p1 150
p2 80
p3 200
p4 350
p5 20

Sample Output 1

p2 180
p5 400
p1 450
p3 550
p4 800

Answer 1

CODE

import java.io.IOException;
import java.io.InputStream;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Scanner;

class Process {
   private String name;
   private int time;
  
   public Process(String name, int time) {
       this.name = name;
       this.time = time;
   }
  
   public int getTime() {
       return time;
   }

   public void setTime(int time) {
       this.time = time;
   }

   public String getName() {
       return name;
   }
  
  
}
public class RoundRobin {

   public static void main(String[] args) {
      
       // scanner for input.
       Scanner s = new Scanner(System.in);
       // accept number of processes.
       int numberOfProcesses = s.nextInt();
       // accept time quantum.
       int timeQuantum = s.nextInt();
      
       // declare queue for processes.
       Queue<Process> processes = new LinkedList<Process>();
      
       // fill the queue form the input.
       for (int i = 0; i<numberOfProcesses; i++) {
           String namei = s.next();
           int timei = s.nextInt();
          
           Process processi = new Process(namei, timei);
           processes.add(processi);
       }
      
       // intialize current ongoing time.
       int currTime = 0;
       // check if process(Queue) is empty
       while(!processes.isEmpty()) {
           // get the head of queue and remove from queue.
           Process p = processes.poll();
           // if the current process is greater than time quantum
           // subtract its remaining time. and add the current time.
           // add the process back to queue.
           if (p.getTime() > timeQuantum) {
               p.setTime(p.getTime() - timeQuantum);
               currTime += timeQuantum;
               processes.add(p);
           }
           // Else add the current time and display the output.
           else {
               currTime += p.getTime();
               System.out.println(p.getName() + " " + currTime);
           }
       }
   }
}

OUTPUT