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

char* del_elem(const char list[], int len, int pos)
{
  char* temp = malloc((len - 1) * sizeof(char));

  memcpy(temp, list, pos * sizeof(char));
  memcpy(&temp[pos], &list[pos+1], len - pos);

  return temp;
}

void perm(char current_string[], int current_position, const char alphabet[], int len)
{
  if(len != 0)
    for(int i = 0; i < len; i++)
    {
      current_string[current_position] = alphabet[i];
      perm(current_string, current_position + 1, del_elem(alphabet, len, i), len - 1);
    }
  else
    printf("%s\n", current_string);
}

void print_permutation(const char alphabet[], int len)
{
  char* temp = calloc(len, sizeof(char));

  perm(temp, 0, alphabet, len);
}

int main(void)
{
  char alphabet[] = {'a', 'b', 'c', 'd'};

  print_permutation(alphabet, sizeof(alphabet) / sizeof(alphabet[0]));

  return 0;
}