private static void divideArr4MergeSort(int[] arr, int left, int right){
		if(left < right){
			int middle = (left + right)/2;
			divideArr4MergeSort(arr, left, middle);
			divideArr4MergeSort(arr, middle+1, right);
			merge(arr, left, middle, right);
		}
	}// a method of merge sort