1. Prepared By:
Nik Fatinah Binti N. Mohd Farid (2012790807)
Hanis Salwan Bt Mobidin(2012144449)
Assignment 2
Merge Sort Using Recursive
Decomposition Technique

2. Problem
 Find a sorted list of element in non-
decreasing order.
 Elements can be in positive or negative
integers.

3. The Decomposition Technique and
Mapping Technique Used
 Recursive decomposition technique was
implemented to solve this problem.
 Merge sort apply a divide and conquer algorithm.
 Merge sort work by dividing the unsorted list into
n sublists, each having 1 element.
 Repeatedly ,merge sublists to produce a new
sublists until there is only 1 sublist remaining.
 Mapping Technique: Since this is a serial
program, no mapping technique used.

4. The Program Structurejava
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Iterator;
public class MergeSort {
public static int[] mergeSort(int [] list) {
if (list.length <= 1) {
return list;
}

5. // Split the array in half
int[] first = new int[list.length / 2];
int[] second = new int[list.length - first.length];
System.arraycopy(list, 0, first, 0, first.length);
System.arraycopy(list, first.length, second, 0, second.length);
// Sort each half
mergeSort(first);
mergeSort(second);
// Merge the halves together, overwriting the original array
merge(first, second, list);
return list;

6. private static void merge(int[] first, int[] second, int []
result) {
// Merge both halves into the result array
// Next element to consider in the first array
int iFirst = 0;
// Next element to consider in the second array
int iSecond = 0;
// Next open position in the result
int j = 0;

7. // As long as neither iFirst nor iSecond is past the end, move the
// smaller element into the result.
while (iFirst < first.length && iSecond < second.length) {
if (first[iFirst] < second[iSecond]) {
result[j] = first[iFirst];
iFirst++;
} else {
result[j] = second[iSecond];
iSecond++;
}
j++;
}
// copy what's left
System.arraycopy(first, iFirst, result, j, first.length - iFirst);
System.arraycopy(second, iSecond, result, j, second.length -
iSecond);
}

8. public static void main(String args[]) throws Exception
{
String list="";
int i=0,n=0;
MergeSort s= new MergeSort();
ArrayList<Integer> arrlist=new ArrayList<Integer>();
System.out.println(" ");
System.out.println(" ");
System.out.println("Please enter the list of elements,one element
per line");
System.out.println(" write 'STOP' when list is completed ");
BufferedReader bf=new BufferedReader(new
InputStreamReader(System.in));
while(!(list=bf.readLine()).equalsIgnoreCase("stop")){
int intelement=Integer.parseInt(list);
arrlist.add(intelement);
}

9. int elementlist[] = new int[arrlist.size()];
Iterator<Integer> iter = arrlist.iterator();
for (int j=0;iter.hasNext();j++) {
elementlist[j] = iter.next();
}
elementlist=mergeSort(elementlist);
System.out.println(" ");
System.out.println(" ");
System.out.println(" ");
System.out.println("Values after Merge Sort : ");
for (int j=0;j<elementlist.length;j++) {
System.out.println(elementlist[j]+" ");
}
}
}

10. Illustration of the Graph
100 45 67 34 23 100
100 45 67 34 23 100
100 45 67 34 23 100
45 67
45 67
45 67 100
23 100
23 100
23 34 100
23 34 45 67 100 100
Merge Sort
Algorithm
Merge Algorithm

11. The Output

12. Reference
 http://javahungry.blogspot.com/2013/06/java-
sorting-program-code-merge-sort.html