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

#define ELEMENT_NR 20
#define ARRAY_LEN(x) (sizeof(x) / sizeof((x)[0]))
const char *notation = "Shell Sort Big O Notation:\
						\n--> Best Case: O(n log(n)) \
						\n--> Average Case: depends on gap sequence \
						\n--> Worst Case: O(n)";

void show_data(int arr[], int len)
{
    int i;

    for (i = 0; i < len; i++)
        printf("%3d ", arr[i]);
    printf("\n");
}

void swap(int *a, int *b)
{
    int tmp;

    tmp = *a;
    *a = *b;
    *b = tmp;
}

void shellSort(int array[], int len)
{
    int i, j, gap;

    for (gap = len / 2; gap > 0; gap = gap / 2)
        for (i = gap; i < len; i++)
            for (j = i - gap; j >= 0 && array[j] > array[j + gap]; j = j - gap)
                swap(&array[j], &array[j + gap]);
}

/**
 * Optimized algorithm - takes half the time as other
 **/
void shell_sort2(int array[], int LEN)
{
    const int gaps[] = {701, 301, 132, 57, 23, 10, 4, 1};
    const int gap_len = 8;
    int i, j, g;

    for (g = 0; g < gap_len; g++)
    {
        int gap = gaps[g];
        for (i = gap; i < LEN; i++)
        {
            int tmp = array[i];

            for (j = i; j >= gap && (array[j - gap] - tmp) > 0; j -= gap)
                array[j] = array[j - gap];
            array[j] = tmp;
        }
    }
#ifdef DEBUG
    for (i = 0; i < LEN; i++)
        printf("%s\t", data[i]);
#endif
}

int main(int argc, char *argv[])
{
    int i;
    int array[ELEMENT_NR];
    int range = 500;
    int size;
    clock_t start, end;
    double time_spent;

    srand(time(NULL));
    for (i = 0; i < ELEMENT_NR; i++)
        array[i] = rand() % range + 1;

    size = ARRAY_LEN(array);

    show_data(array, size);
    start = clock();
    shellSort(array, size);
    end = clock();
    time_spent = (double)(end - start) / CLOCKS_PER_SEC;

    printf("Data Sorted\n");
    show_data(array, size);

    printf("%s\n", notation);
    printf("Time spent sorting: %f\n", time_spent);

    return 0;
}