Código de permutaciones

// C program to print all permutations with duplicates allowed 
#include <stdio.h> 
#include <string.h> 
#define OK	1
#define KO	0

  
/* Function to swap values at two pointers */
void swap(char *x, char *y) 
{ 
    char temp; 
    temp = *x; 
    *x = *y; 
    *y = temp; 
} 
  
/* Function to print permutations of string 
   This function takes three parameters: 
   1. String 
   2. Starting index of the string 
   3. Ending index of the string. */
void permute(char *a, int l, int r) 
{ 
   int i; 
   if (l == r) 
     printf("%s\n", a); 
   else
   { 
       for (i = l; i <= r; i++) 
       { 
          swap((a+l), (a+i)); 
          permute(a, l+1, r); 
          swap((a+l), (a+i)); //backtrack 
       } 
   } 
} 
  
/* Driver program to test above functions */
int main(int argc, char *argv[]) 
{ 
  if ((argc != 2) || (strlen(argv[1]) > 10))
  {
    printf("Utilización: %s Cadena\n", argv[0]);
    printf("'Cadena' no puede tener más de 10 caracteres.\n");
    return KO;
  }
    char str[27];
    strcpy(str, argv[1]);
    int n = strlen(str); 
    permute(str, 0, n-1); 
    return OK; 
}