计算Java快速排序的数据比较

Question

I'm trying to count the number of data comparisons in this quick sort algorithm, but am surely incrementing too often as my expected output is much lower than what I am currently getting. Here, i've incremented in partition's for loop and also every time recQuickSort is called. What am I missing?

private void swap(T[] list, int first, int second)
{
     T temp;
     temp = list[first];
     list[first] = list[second];
     list[second] = temp;
     swapsNo++;
}


public void quickSort(T[] list, int length)
{
    recQuickSort(list, 0, length - 1);
}


private int partition(T[] list, int first, int last)
{
    T pivot;

    int smallIndex;

    swap(list, first, (first + last) / 2);

    pivot = list[first];
    smallIndex = first;


    for (int index = first + 1; index <= last; index++)
    {
        Comparable<T> compElem = (Comparable<T>) list[index];
        //Trying to increment comparisons for every time element compared to pivot
        compsNo++;
        if (compElem.compareTo(pivot) < 0)
        {
            smallIndex++;
            swap(list, smallIndex, index);

        }
    }

    swap(list, first, smallIndex);

    return smallIndex;
}



private void recQuickSort(T[] list, int first, int last)
{
    //Trying to increment comparisons every time, as first and last are compared
    compsNo++;
    if (first < last)
    {
        int pivotLocation = partition(list, first, last);
        recQuickSort(list, first, pivotLocation - 1);
        recQuickSort(list, pivotLocation + 1, last);

    }
}

Answer 1

From the first look of it i dont see where you would be counting extra comparisons. The easiest way to do these type of counting though is to create a CountingComparator class that increments on every compare.

class CountingComparator<T extends Comparable<T>> extends Comparator<T> {

      private int count = 0;
      public int compare(T o1, T o2) {
        ++count;
        return o1.compareTo(o2);
      }

      public int getCount() { return count; }
}

Also if your T would be bound to Comparable you coupd avoid the casts