Permutations using the algorithms described http://www.quickperm.org/pseudo2.php

perm.c

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

#define SZ_ARRAY    5

void swap_array(uint64_t arr[], uint64_t i, uint64_t j)
{
    arr[i] ^= arr[j];
    arr[j] ^= arr[i];
    arr[i] ^= arr[j];
}

void circular_shift_to_left(uint64_t arr[], uint64_t sz)
{
    for (uint64_t i = 0;i<sz-1;i++)
        swap_array(arr, i, i+1);
}

void circular_shift_to_left_by(uint64_t arr[], uint64_t sz, uint64_t num_shift)
{
    for (uint64_t s = 0;s<num_shift;s++)
    {
        for (uint64_t i = 0;i<sz-1;i++)
            swap_array(arr, i, i+1);
    }
}

void print_array(uint64_t arr[], uint64_t sz)
{
    for (uint64_t i = 0;i<sz;i++)
        fprintf(stdout, "%ju", arr[i]);
    fprintf(stdout, "\n");
}

void algo1(const uint64_t arr[], uint64_t sz)
{
    uint64_t a[SZ_ARRAY] = {0};
    uint64_t p[SZ_ARRAY] = {0};
    memcpy(a, arr, sz*sizeof(uint64_t));

    for (uint64_t i = 0;i<sz;i++)
        p[i] = i;

    uint64_t i = 1;

    while(i < sz)
    {
        p[i]--;
        uint64_t j = 0;

        if (i%2 != 0)
            j = p[i];

        swap_array(a, j, i);
        print_array(a, sz);

        i = 1;

        while(p[i] == 0)
        {
            p[i] = i;
            i++;
        }
    }

}


void algo2(const uint64_t arr[], uint64_t sz)
{
    uint64_t counter = 0;
    uint64_t a[SZ_ARRAY] = {0};
    uint64_t p[SZ_ARRAY] = {0};
    memcpy(a, arr, sz*sizeof(uint64_t));

    for (uint64_t i = 0;i<sz;i++)
        p[i] = i;

    uint64_t i = 1;
    uint64_t j = 0;

    while(i < sz)
    {
        if (p[i] > 0)
        {
            p[i]--;
            j = 0;

            if (i%2 != 0)
                j = p[i];

            swap_array(a, j, i);
            print_array(a, sz);
            counter++;

            i = 1;
        }
        else
        {
            p[i] = i;
            i++;
        }
    }

    fprintf(stdout, "Permutations counted for size %ju is %ju.\n", sz, counter);
}

// It's not working
void myalgo(const uint64_t arr[], uint64_t sz)
{
    uint64_t counter = 0;
    uint64_t a[SZ_ARRAY] = {0};
    memcpy(a, arr, sz*sizeof(uint64_t));

    uint64_t k = 0;
    uint64_t tmp[SZ_ARRAY] = {0};
    memcpy(tmp, a, sz*sizeof(uint64_t));
    while(k<sz-2)
    {
        for (uint64_t i = 0;i<sz-1;i++)
        {
            swap_array(tmp, i, i+1);
            print_array(tmp, sz);
            counter++;
        }
        for (uint64_t i = sz-2;i>1;i--)
        {
            swap_array(tmp, i-1, i);
            print_array(tmp, sz);
            counter++;
        }

        k++;
    }

    fprintf(stdout, "Permutations counted for size %ju is %ju.\n", sz, counter);
}

int main(int argc, char *argv[])
{
    // Initial array
    const uint64_t arr[SZ_ARRAY] = {1, 2, 3, 4, 5};

    algo2(arr, SZ_ARRAY);
    myalgo(arr, SZ_ARRAY);
}