Answer:
Here is the first routine:
void permute( const string &str ) { // function with one parameter
int low = 0;
int high = str.length();
permute(str, low, high);
}
Or you can directly call it as:
permute(str, 0, str.length());
Explanation:
The second routine:
void permute( const string &str, int low, int high)
//function with three parameters
{ string str1 = str;
if ( low == high ) { //base case when last index is reached
for (int i = 0; i <= high; ++i)
cout << str1[i]; } //print the strings
else {
for (int i=low; i<high; ++i) { // if base case is not reached
string temp = str1; //fix a character
swap( str1[i], str1[low] );
//swap the values
permute( str1, low + 1, high ); //calling recursive function (recursion case)
swap( str1[i], str1[low] ); } } } //swap again to go to previous position
In this function the following steps are implemented:
A character is fixed in the first position.
Rest of the characters are swapped with first character.
Now call the function which recursively repeats this for the rest of the characters.
Swap again to go to previous position, call the recursive function again and continue this process to get all permutations and stop when base condition is reached i.e. last index is reached such that high==low which means both the high and low indices are equal.
You can write a main() function to execute these functions.
int main() {
string str;
cout << "Enter a string: ";
cin >> str;
permute(str); }
