Quicksoft Notes - 2011/06/01

Using the partition, the first pivot is using the a[right] or a[left+(right-left)/2]. For the latter, remember to swap the a[left+(right-left)/2] to the a[right] firstly.

Then

void quicksort(int* array, int left, int right)

{

if (right > left) // subarray of 0 or 1 elements already sorted

{

    //select a pivotIndex in the range left ≤ pivotIndex ≤ right
    // see Choice of pivot for possible choices

    int pivotIndex = left+(right-left)/2;

    int pivotNewIndex = inplace_partition(array, left, right,pivotIndex); // element at pivotNewIndex is now at its final position

    quicksort(array, left, pivotNewIndex - 1); // recursively sort elements on the left of pivotNewIndex

    quicksort(array, pivotNewIndex + 1, right); // recursively sort elements on the right of pivotNewIndex

}

}

One interesting thing for swap:

Can you see any problem for such code looking wise?

void swap(int& a, int& b)

{

a = a + b;

b = a - b;

a = a - b;

}

Reference: Introduction to Algorithms, Chapter 7.1.