2.2.quick-sort.c

#include <stdio.h>
#include <stdlib.h>

#define LENGTH_OF_ARRAY(array) (sizeof(array) / sizeof(array[0]))

/* swap: interchange v[i] and v[j] */
void swap(int v[], int i, int j)
{
    int temp;
    temp = v[i];
    v[i] = v[j];
    v[j] = temp;
}

/* quicksort: sort v[0]..v[n-1] into increasing order */
void quicksort(int v[], int n)
{
    int i, last;
    if (n <= 1) /* nothing to do */
        return;
    swap(v, 0, rand() % n); /* move pivot elem to v[0] */
    last = 0;
    for (i = 1; i < n; i++) /* partition */
        if (v[i] < v[0])
            swap(v, ++last, i);
    swap(v, 0, last);                      /* restore pivot */
    quicksort(v, last);                    /* recursively sort */
    quicksort(v + last + 1, n - last - 1); /* each part */
}

int main(int argc, char const *argv[])
{
    int arr[7] = {1, 4, 5, 7, 3, 4, 6};
    quicksort(arr, LENGTH_OF_ARRAY(arr));

    for (size_t i = 0; i < LENGTH_OF_ARRAY(arr); i++)
        printf("%d ", arr[i]);

    return 0;
}