Question

Write a c program to implement Quicksort for arrays of length 16, as described in the textbook, taking always as the pivot the last element of the corresponding subarray. Define a variable COUNTER in your program that keeps track of the total number of comparisons among the elements in the array needed to sort the array Run your program 100 times using as inputs 100 arrays of real numbers in the interval [0, 11 generated randomly. Find the sample average (Counter1+Counter 2+Counter100)/100

Answer 1

#include<stdio.h>

void quicksort(double *,int,int, int *);

int partition(double *,int,int, int *);

int main()

{

    int n = 16;

    int total_comparison = 0;

    int i;

   

    for( i = 0 ; i < 100 ; i++ )

    {

        double arr[n];

        int comparison = 0;

        int i;

       

        for( i = 0 ; i < 16 ; i++ )

            // generate random number between o to 1

            arr[i] = (double)( rand() % 32767 ) / 32767.0;

           

        quicksort(arr, 0, n - 1, &comparison);

       

        total_comparison += comparison;

    }

   

    // compute average

    double avg = (double)total_comparison / 100.0;

           

    printf("Average : %lf", avg);

           

    return 0;

}

// function to sort using quick sort

void quicksort(double *arr,int p,int r, int *comparison)

{

    int q;

   

    if(p<r)

    {

        // create a partition

        q = partition(arr,p,r, comparison);

       

        // sort the left subarray

        quicksort(arr,p,q-1, comparison);

       

        // sort the right subarray

        quicksort(arr,q+1,r, comparison);

    }

}

int partition(double *arr,int p,int r, int *comparison)

{  

    // set pivot

    int pivot = arr[r];

   

    // set the lindex of lower element

    int j, i = p - 1;

    for (j = p; j <= r - 1; j++ )

    {

        (*comparison)++;

       

        // a comparison ahead

        if (arr[j] <= pivot)

        {

            // increment smaller element index

            i++;

           

            // swap the contents of i and j position

            double temp=arr[i];

            arr[i]=arr[j];

            arr[j]=temp;

        }

    }

   

    double temp = arr[i + 1];

    arr[i+1] = arr[r];

    arr[r] = temp;

   

    return i + 1;

}

Sample Output

erage : 120.00000 0