Question

I’ve struggling to implement a lexicographical merge sort method for the past couple of days. i’ve come up to a point were i get: ArrayIndexOutOfBounds error and i dont know why. i f anyone could take a look and tell me what might be wrong.i tried debugging but all the values seem correct.

Reply to aix: it happens at this point temp[index1] = array[min + index1] ;
These are the values at that exact time:

array :String[5] (5 entries originating from a text file)
min : 0
max : 1
size : 2
pivot : 0
temp : Comparable<T>[2]  (both entries null)

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 5
    at Merge.mergeSort(Merge.java:47)
    at Merge.mergeSort(Merge.java:43)
    at Merge.Sort(Merge.java:20)
    at Sort.main(Sort.java:96)

Line 43:

mergeSort(array, pivot + 1, max) ;

Line 47:

temp[index1] = array[min + index1] ;

The code:

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;

public class Merge 
{
    public static void Sort (LinkedList listIn, int size) throws Exception
    {
        String[] mArray = new String[size] ;
        String textContent = null ;
        File outputFile ;

        //copy the list values in the array
        for (int i = 0 ; i < size ; i++)
        {
             mArray [i] = listIn.get(i).printNode();
        }

        mergeSort(mArray, 0, mArray.length) ;       


    }

    public static <T extends Comparable<? super T>> void mergeSort(T[] array, int min, int max)
    {
        T[] temp ;
        int index1 ;
        int left ;
        int right ;

        // if array is of size 1

        if (min == max)
            return ;

        // find length and midpoint
        int size = max - min + 1 ;
        int pivot = (min + max) / 2 ;
        temp = (T[]) (new Comparable[size]) ;

        mergeSort(array, min, pivot) ;
        mergeSort(array, pivot + 1, max) ;

        for (index1 = 0 ; index1 < size ; index1++)
        {
            temp[index1] = array[min + index1] ;
        }

        left = 0 ;
        right = pivot - min + 1 ;
        for (index1 = 0 ; index1 < size ; index1++)
        {
            if (right <= max - min)
                if (left <= pivot - min)
                    if (temp[left].compareTo(temp[right]) > 0)
                        array[index1 + min] = temp[right++] ;
                    else
                        array[index1 + min] = temp[left++] ;
                else
                    array[index1 + min] = temp[right++] ;
            else
                array[index1 + min] = temp[left++] ;
        }
    }


}

Answer 1

Your Sort method is sending the wrong values when you first invoke merge. Change mergeSort(mArray, 0, mArray.length) to mergeSort(mArray, 0, mArray.length-1);