Question

Write a java program that implements the following disk-scheduling algorithms: a. FCFS b. SSTF c. SCAN Your program will service a disk with 5000 cylinders numbered 0 to 4999. The program will generate a random series of 1,000 cylinder requests and service them according to each of nth algorithms listed above. The program will be passed the initial position of the disk head and report the total amount of head movement required by the algorithm.

Answer 1

Here is the code (Please read comments for explanation) :-

1 2 import java.util.Random; import java.util.Arrays; import java.util.Scanner; class Main{ public static int[] remove TheElement(int[] arr, int index) // If the array is empty // or the index is not in array range Il return the original array if (arr == null || index < 0 || index >= arr.length) { return arr; // Create another array of size one less int[] anotherArray = new int[arr.length - 1]; // Copy the elements except the index // from original array to the other array for (int i = 0, k = 0; i < arr.length; i++) { // if the index is // the removal element index if (i == index) { continue;

// if the index is not // the removal element index anotherArray[k++] = arr[i]; Il return the resultant array return anotherArray; int FCFS(int[] arr, int size) { int totalmoves=0; for (int i=0;i<size-1;i++) { totalmoves+=Math.abs(arr[i]-arr[i+1]); } return totalmoves; int SSTF(int[] arr, int size, int firstNum) { int[] temparr=new int[size]; // duplicate array, for (int i=0;i<size ;i++) { // store in duplicate array temparr[i]=arr[i]; int totalmoves=0; int totalNumScaned=0; Arrays.sort(temparr); //Sort temparr in asending order

int index=0; for (int i=0;i size ;i++) { if (temparr[i]==firstNum) { index=i; break; while (totalNumScaned size) { if (index>0 && index<size-totalNumScaned-1) { // Calculate difference between current and left number int leftdifference-Math.abs(temparr[index] -temparr[index-1]); // Calculate difference between current and right number int rightDifference=Math.abs(temparr[index] -temparr[index+1]); // Check which neighbour is near (left or right) if (leftDifference rightDifference) { //If left neighbour is near totalNumScaned++; totalmoves+=Math.abs(temparr[index] -temparr[index-1]); // Remove current element temparr=removeTheElement(temparr, index); // Jump to left index--; else { //If right neighbour is near totalNumScaned++; totalmoves+=Math.abs(temparr[index] -temparr[index+1]);

temparr=remove TheElement(temparr , index); else if(index>0 && index<=size-totalNumScaned -1){ totalNumScaned++; totalmoves+=Math.abs(temparr[index] -temparr[index-1]); // Remove current element temparr=removeTheElement(temparr ,index); index--; else if(index>=0 && index<size-totalNumScaned-1) { totalNumScaned++; totalmoves+=Math.abs(temparr[index] -temparr[index+1]); // Remove current element temparr=removeTheElement(temparr ,index); if (totalNumScaned==size-1) { remove TheElement(temparr, index); totalNumScaned++; 99 return totalmoves; 100 101 102 103 104 int SCAN(int[] arr, int size, int firstNum) {

105 106 107 108 109 110 111 112 int totalmoves=0; Arrays.sort(arr); int index=0; for (int i=0;i<size ;i++) { if (arr[i]==firstNum) { index=i; break; 113 114 115 116 if (index==0 || index==size-1) { return arr[size-1] -arr[0]; 117 totalmoves+=arr[size-1] -arr[index]; totalmoves+=arr[size-1] -arr[@]; totalmoves+=arr[index-1] -arr[0]; return totalmoves; 118 119 120 121 122 123 124 125 126 127 128 129 130 public static void main(String[] args) { int[] arr=new int[1000); Random rand = new Random(); //To generate random number for (int i=0;i<arr.length; i++) { // Generate random number between 0,4999 arr[i]=rand.nextInt(5000); int firstNum=arr[0];

132 133 134 135 136 137 138 139 140 Main m=new Main(); System.out.print("Total moves in FCFS= "); System.out.println(m.FCFS(arr, arr.length)); System.out.print("Total moves in SSTF= "); System.out.println(m.SSTF(arr, arr.length, firstNum)); System.out.print("Total moves in SCAN= "); System.out.println(m.SCAN(arr, arr.length, firstNum)); }

Here is the output : -

Total moves in FCFS= 1651345 Total moves in SSTF= 6410 Total moves in SCAN= 9976 Total moves in FCFS= 1642693 Total moves in SSTF= 5601 Total moves in SCAN= 9988 Total moves in FCFS= 1646600 Total moves in SSTF= 8955 Total moves in SCAN= 9920 Total moves in FCFS= 1649478 Total moves in SSTF= 9433 Total moves in SCAN= 9985 Total moves in FCFS= 1657925 Total moves in SSTF= 6083 Total moves in SCAN= 9987

Here is the code in text format : -

import java.util.Random;
import java.util.Arrays;
import java.util.Scanner;
class Main{

   public static int[] removeTheElement(int[] arr, int index)
{
  
// If the array is empty
// or the index is not in array range
// return the original array
if (arr == null || index < 0 || index >= arr.length) {
return arr;
}
  
// Create another array of size one less
int[] anotherArray = new int[arr.length - 1];
  
// Copy the elements except the index
// from original array to the other array
for (int i = 0, k = 0; i < arr.length; i++) {
  
// if the index is
// the removal element index
if (i == index) {
continue;
}
  
// if the index is not
// the removal element index
anotherArray[k++] = arr[i];
}
  
// return the resultant array
return anotherArray;
}

   int FCFS(int[] arr, int size){
       int totalmoves=0;
       for (int i=0;i<size-1;i++){
           totalmoves+=Math.abs(arr[i]-arr[i+1]);
       }
       return totalmoves;
   }
   int SSTF(int[] arr, int size, int firstNum){
       int[] temparr=new int[size]; //duplicate array
       for (int i=0;i<size ;i++ ) { // store in duplicate array
           temparr[i]=arr[i];
       }
       int totalmoves=0;
       int totalNumScaned=0;
       Arrays.sort(temparr); //Sort temparr in asending order
       int index=0;
       for (int i=0;i<size ;i++ ) {
           if (temparr[i]==firstNum) {
               index=i;
               break;
           }
       }

       while (totalNumScaned<size) {
           if (index>0 && index<size-totalNumScaned-1) {
               // Calculate difference between current and left number
               int leftDifference=Math.abs(temparr[index]-temparr[index-1]);
               // Calculate difference between current and right number
               int rightDifference=Math.abs(temparr[index]-temparr[index+1]);
               // Check which neighbour is near (left or right)
               if (leftDifference<rightDifference) { //If left neighbour is near
                   totalNumScaned++;
                   totalmoves+=Math.abs(temparr[index]-temparr[index-1]);
                   // Remove current element
                   temparr=removeTheElement(temparr, index);
                   // Jump to left
                   index--;
               }
               else { //If right neighbour is near
                   totalNumScaned++;
                   totalmoves+=Math.abs(temparr[index]-temparr[index+1]);
                   temparr=removeTheElement(temparr ,index);
               }
           }
           else if(index>0 && index<=size-totalNumScaned-1){
               totalNumScaned++;
               totalmoves+=Math.abs(temparr[index]-temparr[index-1]);
               // Remove current element
               temparr=removeTheElement(temparr ,index);
               index--;
           }
           else if(index>=0 && index<size-totalNumScaned-1){
               totalNumScaned++;
               totalmoves+=Math.abs(temparr[index]-temparr[index+1]);
               // Remove current element
               temparr=removeTheElement(temparr ,index);
           }
           if (totalNumScaned==size-1) {
               removeTheElement(temparr, index);
               totalNumScaned++;
           }
       }
       return totalmoves;

   }
  
   int SCAN(int[] arr, int size, int firstNum){
       int totalmoves=0;
       Arrays.sort(arr);
       int index=0;
       for (int i=0;i<size ;i++ ) {
           if (arr[i]==firstNum) {
               index=i;
               break;
           }
       }
       if (index==0 || index==size-1) {
           return arr[size-1]-arr[0];
       }
       totalmoves+=arr[size-1]-arr[index];
       totalmoves+=arr[size-1]-arr[0];
       totalmoves+=arr[index-1]-arr[0];
       return totalmoves;
   }

   public static void main(String[] args) {
       int[] arr=new int[1000];
       Random rand = new Random(); //To generate random number
       for (int i=0;i<arr.length;i++) {
           // Generate random number between 0,4999
           arr[i]=rand.nextInt(5000);
       }
       int firstNum=arr[0];

       Main m=new Main();
       System.out.print("Total moves in FCFS= ");
       System.out.println(m.FCFS(arr,arr.length));
       System.out.print("Total moves in SSTF= ");
       System.out.println(m.SSTF(arr,arr.length,firstNum));
       System.out.print("Total moves in SCAN= ");
       System.out.println(m.SCAN(arr,arr.length,firstNum));
   }
}