Quicksort (C++)

 NEW!  Quicksort (C++/ Java/ C/ Prolog/ javaScript)

• Complexity of Quicksort
• Complexity of sorting algorithms
• Simulation of Quicksort

quickSort.cpp

#include <iostream>

void quickSort(int a[], int first, int last);
int pivot(int a[], int first, int last);
void swap(int& a, int& b);
void swapNoTemp(int& a, int& b);
void print(int array[], const int& N);

using namespace std;

int main()
{
    int test[] = { 7, -13, 1, 3, 10, 5, 2, 4 };
    int N = sizeof(test)/sizeof(int);

    cout << "Size of test array :"  << N << endl;

    cout << "Before sorting : " << endl;
    print(test, N);

    quickSort(test, 0, N-1);

    cout << endl << endl << "After sorting : " << endl;
    print(test, N);
    
    return 0;
}

/**
 * Quicksort.
 * @param a - The array to be sorted.
 * @param first - The start of the sequence to be sorted.
 * @param last - The end of the sequence to be sorted.
*/
void quickSort( int a[], int first, int last ) 
{
    int pivotElement;

    if(first < last)
    {
        pivotElement = pivot(a, first, last);
        quickSort(a, first, pivotElement-1);
        quickSort(a, pivotElement+1, last);
    }
}

/**
 * Find and return the index of pivot element.
 * @param a - The array.
 * @param first - The start of the sequence.
 * @param last - The end of the sequence.
 * @return - the pivot element
*/
int pivot(int a[], int first, int last) 
{
    int  p = first;
    int pivotElement = a[first];

    for(int i = first+1 ; i <= last ; i++)
    {
        /* If you want to sort the list in the other order, change "<=" to ">" */
        if(a[i] <= pivotElement)
        {
            p++;
            swap(a[i], a[p]);
        }
    }

    swap(a[p], a[first]);

    return p;
}


/**
 * Swap the parameters.
 * @param a - The first parameter.
 * @param b - The second parameter.
*/
void swap(int& a, int& b)
{
    int temp = a;
    a = b;
    b = temp;
}

/**
 * Swap the parameters without a temp variable.
 * Warning! Prone to overflow/underflow.
 * @param a - The first parameter.
 * @param b - The second parameter.
*/
void swapNoTemp(int& a, int& b)
{
    a -= b;
    b += a;// b gets the original value of a
    a = (b - a);// a gets the original value of b
}

/**
 * Print an array.
 * @param a - The array.
 * @param N - The size of the array.
*/
void print(int a[], const int& N)
{
    for(int i = 0 ; i < N ; i++)
        cout << "array[" << i << "] = " << a[i] << endl;
} 

This code was developed by me, G. Samaras.

Notice, that I used as little C++ as possible, so that one can easy interchange between C and C++.
Have questions about this code? Comments? Did you find a bug? Let me know! 😀
Page created by G. (George) Samaras (DIT)