// input array is assumed to be sorted  public int BinarySearch(int[] arr, int x)  {      if (arr.Length == 0)          return -1;         int mid = arr.Length / 2;         if (arr[mid] == x)          return mid;         if (x < arr[mid])          return BinarySearch(GetSubArray(arr, 0, mid - 1), x);      else      {          int _indexFound = BinarySearch(GetSubArray(arr, mid + 1, arr.Length - 1), x);          if (_indexFound == -1)              return -1;          else              return mid + 1 + BinarySearch(GetSubArray(arr, mid + 1, arr.Length - 1), x);      }  }        public int[] GetSubArray(int[] arr, int start, int end)  {      List<int> _result = new List<int>();      for (int i = start; i <= end; i++)      {          _result.Add(arr[i]);      }      return _result.ToArray();  }