MergeSort

I am trying to implement recursive mergesort algorithm and it is almost done the only thing is that if i want to mergesort ( 7, 1 ,2, 3, 5, 6, 8, 4) when i run the program my output is (0, 0, 1, 2, 3, 4, 5, 6, 7, 8)

What is wrong with my code???

Code :

---

import java.util.*;
import java.io.*;
 
public class MergeSort
{
 
public static void mergeSort(double[] a, int length)
   {  
     Sort(a, 0, a.length - 1);
   }
public static void Sort(double[] a, int left, int right)
   {  
     if (left < right)
     {
      int mid = (left + right) / 2;
       // sort the first and the second half
      Sort(a, left, mid);
      Sort(a, mid + 1, right);
      merge(a, left, mid, right);
     }
   }
   public static void merge(double[] a, int left, int mid, int right)
   {  
 
      double[] b = new double[right - left + 1]; // merge both halves into a temporary array b
 
      int index1 = left;         // next element to consider in the first range
      int index2 = mid + 1;
      int last = right;
      int index = 0;             // next open position in b
 
      // as long as neither i1 nor i2 past the end, move the smaller into b
      while(index1 <= mid && index2 <= last)
      {  
        if(a[index1] < a[index2])
         {  
          b[index] = a[index1];
            index1++;
         }
         else
         { 
           b[index] = a[index2];
            index2++;
         }
         index++;
      }
 
      // note that only one of the two while loops
      // below is executed
 
      // copy any remaining entries of the first half
      while (index1 <= mid)
      { 
        b[index] = a[index1];
         index1++;
         index++;
      }
 
      // copy any remaining entries of the second half
      while (index2 <= last)
      {  
        b[index] = a[index2];
         index2++;
         index++;
      }
      int s = 0;
      // copy back from the temporary array
      for(int i = left; i <= right; i++)
      {
         a[i] = b[s];
         s++;
      }
   }
 
public static void main(String[] args)throws FileNotFoundException
{
  Scanner input = new Scanner(new FileReader("input.txt"));
 
  int count = 0;
  int numOfElements = 0;  
  double[] array = new double[10];
 
 
  while(input.hasNextDouble())
  {
    array[count] = input.nextDouble();
    count++;
  }
        System.out.println("Unsorted Array");
    for(int i = 0; i < count; i++)
    {
       System.out.print(array[i] + " ");
  }
    System.out.println();
    mergeSort(array, array.length);
    System.out.println("Sorted Array");
    for(int i = 0; i < count; i++)
    {
      System.out.print(array[i] + " ");
    }
 
input.close();
 }
}

---

correction my output when i run the program is (0,0,1,2,3,4,5,6) so it leaves out that last two integers of my array

I don't see any problem with your code right off. When I run your code and manually set the array to be random-ish values, it works. Is it possible you aren't reading what you think you're reading from the file?

Hey m8, you may find the Mergesort I have here: http://www.javaprogrammingforums.com...mergesort.html useful as a reference. It works for the numbers I have tried.

You may also find this psudocode useful:

Code :

---

function mergesort(m)
   var list left, right, result
   if length(m) ≤ 1
       return m
   else
       var middle = length(m) / 2
       for each x in m up to middle - 1
           add x to left
       for each x in m at and after middle
           add x to right
       left = mergesort(left)
       right = mergesort(right)
       if last(left) ≤ first(right) 
          append right to left
          return left
       result = merge(left, right)
       return result
 
function merge(left,right)
   var list result
   while length(left) > 0 and length(right) > 0
       if first(left) ≤ first(right)
           append first(left) to result
           left = rest(left)
       else
           append first(right) to result
           right = rest(right)
   if length(left) > 0 
       append rest(left) to result
   if length(right) > 0 
       append rest(right) to result
   return result

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Source: http://rosettacode.org/wiki/Sorting_...hms/Merge_sort