// method to sort an array, using selection sort.
  public void sort(int[] a) {
    selSort(a, 0);
  }

  // sort all elements in a from a[start]..a[length-1]
  private void selSort(int[] a, int start) {
    if (start < a.length - 1) {
      int smallestIndex = indexOfSmallest(start);

      int temp = a[start];
      a[start] = a[smallestIndex];
      a[smallestIndex] = temp;

      selSort(a, start + 1);
    }
  }

  // Return the smallest element at index start or higher
  private int indexOfSmallest(int[] a, int start) {
    int smallestIndex = start;
    for (int i = start + 1; i < a.length; i++) {
      if (a[i] < a[smallestIndex]) {
        smallestIndex = i;
      }
    }
    return smallestIndex;
  }