Printing all Permutations of a String - C Programming Tutorial

In this c programming tutorial we are going to see a c program to print all permutations of a given string. Now let's see what is a permutation.

A permutation, also called an arrangement number or order, is a rearrangement of the elements of an ordered list S into a one-to-one correspondence with S itself. A string of length n has n! permutation. Source: Mathword

Below are the permutations of string CBA.
ABC, ACB, BAC, BCA, CAB, CBA
Algorithm Paradigm: Backtracking
Time Complexity: O(n*n!)
Please write comments if you find the above codes/algorithms incorrect, or find other ways to solve the same problem.

#include <stdio.h>
#include <string.h>
/* 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()
{
    char str[] = "SHRI";
    int n = strlen(str);
    permute(str, 0, n-1);
    return 0;
}

 Output :