// Pre-condition: str is a valid C String, and k is non-negative and
// less than or equal to the length of str.
// Post-condition: All of the permutations of str with the first k
// characters fixed in their original positions are
// printed. Namely, if n is the length of str, then
// (n-k)! permutations are printed.
void RecursivePermute(char str[], int k) {
int j;
// Base-case: Since all letters are fixed, we can ONLY print
// what's stored in str.
if (k == strlen(str))
printf("%s\n", str);
else {
// Loop through each possible starting letter for index k,
// the first index for which we have a choice.
for (j=k; j<strlen(str); j++) {
// Place the character stored in index j in location k.
ExchangeCharacters(str, k, j);
// Print out all of the permutations with that character
// just chosen above fixed.
RecursivePermute(str, k+1);
// Put the original character that used to be there back
// in its place.
ExchangeCharacters(str, j, k);
}
}
}
static void RecursivePermute(string str, int k, setADT set)
{
int i;
if (k == StringLength(str)) {
AddPtrElement(set, CopyString(str));
} else {
for (i = k; i < StringLength(str); i++) {
ExchangeCharacters(str, k, i);
RecursivePermute(str, k + 1, set);
ExchangeCharacters(str, k, i);
}
}
}