permutations of string Algorithm

//
// C program to print all permutations with repetition
// of characters
//
// The All ▲lgorithms Project
//
// https://allalgorithms.com/strings
// https://github.com/allalgorithms/cpp
//
// Contributed by: Tushar Kanakagiri
// Github: @tusharkanakagiri
//
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/* Following function is used by the library qsort() function
  to sort an array of chars */
int compare(const void *a, const void *b);

/* The main function that recursively prints all repeated
   permutations of  the given string. It uses data[] to store all
   permutations one by one */
void allLexicographicRecur(char *str, char *data, int last, int index)
{
    int i, len = strlen(str);

    // One by one fix all characters at the given index and recur for
    // the/ subsequent indexes
    for (i = 0; i < len; i++)
    {
        // Fix the ith character at index and if this is not the last
        // index then recursively call for higher indexes
        data[index] = str[i];

        // If this is the last index then print the string stored in
        // data[]
        if (index == last)
            printf("%s\n", data);
        else // Recur for higher indexes
            allLexicographicRecur(str, data, last, index + 1);
    }
}

/* This function sorts input string, allocate memory for data (needed
   for allLexicographicRecur()) and calls allLexicographicRecur() for
   printing all  permutations */
void allLexicographic(char *str)
{
    int len = strlen(str);

    // Create a temp array that will be used by allLexicographicRecur()
    char *data = (char *)malloc(sizeof(char) * (len + 1));
    data[len] = '\0';

    // Sort the input string so that we get all output strings in
    // lexicographically sorted order
    qsort(str, len, sizeof(char), compare);

    // Now print all permutaions
    allLexicographicRecur(str, data, len - 1, 0);

    // Free data to avoid memory leak
    free(data);
}

// Needed for library function qsort()
int compare(const void *a, const void *b)
{
    return (*(char *)a - *(char *)b);
}

// Driver program to test above functions
int main()
{
    char str[] = ""; //Enter character array
    printf("All permutations with repetition of %s are: \n",
           str);
    allLexicographic(str);
    return 0;
}