mergeSortWithoutCopy

private static void mergeSort(int[] arr,int begin,int end){


        if(begin>=end)
            return;

        int middle=(begin + end)/2;
        mergeSort(arr,begin,middle);
        mergeSort(arr,middle+1,end);
        merge(arr,begin,middle,end);

    }

    private static void merge(int[] arr,int begin,int middle,int end){

        int firstContainerLimit=middle-begin+1;
        int[] firstContainer=new int[firstContainerLimit];

        int secondContainerLimit=end-middle;
        int[] secondContainer=new int[secondContainerLimit];

        //copy to first container

        for(int i=0;i<firstContainerLimit;i++)
            firstContainer[i]=arr[begin+i];

        for(int i=0;i<secondContainerLimit;i++)
            secondContainer[i]=arr[middle+1+i];


        int i=0;
        int j=0;
        int k=begin;
        while(i< firstContainerLimit && j<secondContainerLimit){

            if(firstContainer[i] <= secondContainer[j]){
                  arr[k++]=firstContainer[i];
                    i++;
            }
            else{
                arr[k++]=secondContainer[j];
                j++;
            }

        }

        while(i<firstContainerLimit)
            arr[k++]=firstContainer[i++];

        while(j<secondContainerLimit)
           arr[k++]=secondContainer[j++];


    }