Print all the permutations of a string in C

Question

I am learning backtracking and recursion and I am stuck at an algorithm for printing all the permutations of a string. I solved it using the bell algorithm for permutation b

Answer 1

The code has 2 problems, both related to n, the assumed length of the string. The code for (j = i; j <= n; j++) { swap((a+i), (a+j)); ... swap in string's null character '\0' and gives code truncated results. Check the original (i == n) which should be (i == (n-1)).

Backtracking is applied by calling swap() twice effective undoing its original swap.

The order of complexity is the same for Bell Algorithm.

#include 

void swap(char *a, char *b) { char t = *a; *a = *b; *b = t; }

void permute(char *a, int i, int n) {
   // If we are at the last letter, print it
   if (i == (n-1)) printf("%s\n", a);
   else {
     // Show all the permutations with the first i-1 letters fixed and 
     // swapping the i'th letter for each of the remaining ones.
     for (int j = i; j < n; j++) {
       swap((a+i), (a+j));
       permute(a, i+1, n);
       swap((a+i), (a+j));
     }
  }
}

char s[100];
strcpy(s, "ABCD");
permute(s, 0, strlen(s));