C++ Permutation with a output length limit and special arguments - c++

Question

I am new to C++ and I am working on a program that will generate a list of all permutations of a string of characters, however I need the ability to limit the length of the output to lets say 5 characters (this will most likely become a variable number set by the user). I have been searching for about a week for something like this and the closest I have gotten is the following code.
Source.cpp:
#include <iostream>;
using namespace std;
void swap(char *fir, char *sec)
{
char temp = *fir;
*fir = *sec;
*sec = temp;
}
/* arr is the string, curr is the current index to start permutation from and size is sizeof the arr */
void permutation(char * arr, int curr, int size)
{
if(curr == size-1)
{
for(int a=0; a<size; a++)
cout << arr[a] << "";
cout << endl;
}
else
{
for(int i=curr; i<size; i++)
{
swap(&arr[curr], &arr[i]);
permutation(arr, curr+1, size);
swap(&arr[curr], &arr[i]);
}
}
}
int main()
{
string next;
char str[] = "abcdefghijklmnopqrstuvwxyz1234567890-";
permutation(str, 0, sizeof(str)-1);
cin.get();
cin.get();
}
This code works however it does not limit the length of the output. It sets the output length to the length of the given string. It also appears it might not account for multiple of the same letter/number in the output (this I am not 100% sure of).
Additionally, I will need to set special rules such as the hypen cannot be the first or last character in the output.
I have attempted to modify the above code by replacing sizeof(str)-1 with 5 however it will only "loop" through the first 5 characters in the string, so anything beyond "e" is not processed.
If anyone can assist on this it would be much appreciated.
EDIT:
Thank you to everyone for their excellent help I am now going to post my final product in case anyone else was trying to do the same thing.
Final Source:
#include <iostream>
#include <string>
#include <sstream>
#include <fstream>
using namespace std;
void swap(char *fir, char *sec)
{
char temp = *fir;
*fir = *sec;
*sec = temp;
}
void permutation(char * arr, int size, char* result, int depth, int limit)
{
ofstream myfile ("permutation.txt", fstream::app);
if(depth == limit)
{
for(int a=0; a<limit; a++){
myfile << result[a] << "";
cout << result[a] << "";
}
myfile << "\n";
cout << endl;
}
else
{
for(int i=0; i<size; i++)
{
result[depth] = arr[i];
permutation(arr, size, result, depth + 1, limit);
}
}
myfile.close();
}
int main()
{
ofstream myfile ("permutation.txt");
myfile << "";
myfile.close();
string answer;
char *rArray;
string startProcess = "N";
std::cout << "Welcome to permutation v1" << endl;
std::cout << "-------------------------" << endl;
std::cout << "Please enter how long the string should be: ";
std::getline (std::cin,answer);
int result = atoi(answer.c_str());
rArray = new char[result];
std::cout << "\n\nThank You!\n" << endl;
std::cout << "Please wait, generating possible character array for length of " << result << "." << endl;
std::cout << "Would you like to proceed? Y = yes & N = no: ";
std::getline (std::cin,startProcess);
char str[] = "abcdefghijklmnopqrstuvwxyz1234567890";
if(startProcess == "Y")
{
permutation(str, sizeof(str)-1, rArray, 0, result);
}
else
{
std::cout << "\n\nOperation Terminated. No permutations being generated..." << endl;
}
cin.get();
return EXIT_SUCCESS;
}

Answer 1

You need to limit the depth of the recursion
To give permutations of characters in the string, using each only once:
void permutation(char * arr, int currsize, intchar* sizeresult, int depth, int limit)
{
if(depth == limit)
{
for(int a=0; a<limit; a++)
cout << arr[a]result[a] << "";
cout << endl;
}
else
{
for(int i=curr;i=0; i<size; i++)
{
swap(&arr[curr],result[depth] &arr[i]);= arr[i];
permutation(arr, curr+1size, sizeresult, depth + 1, limit);
swap(&arr[curr], &arr[i]);
}
}
}
Call like this
permutation(str, 0, sizeof(str)-1, result, 0, 5);
To give permutations of characters in the string, using each character an unlimited number of times:
void permutation(char * arr, int size, char* result, int depth, int limit)
{
if(depth == limit)
{
for(int a=0; a<limit; a++)
cout << result[a] << "";
cout << endl;
}
else
{
for(int i=0; i<size; i++)
{
result[depth] = arr[i];
permutation(arr, size, result, depth + 1, limit);
}
}
}
Call like this
char result[5];
permutation(str, sizeof(str)-1, result, 0, sizeof(result));

Answer 2

This is not a tough job actually. If you can use recursion and a loop within that function you can solve it. I suggest use next_permutation function from the standard library.
The fact is time. Within 3 second you can process permutation for only 8 character. And the condition will be depended to requirement. Suppose in your example you can prune back if you need to omit hyphen in starting or ending.
Pseudo code of my implementation:
char array[] = "abcdee";
char eachPerm[6];
bool usedmatrix[6][6];
Recur(int depth, int n)
{
// you can return from here if this is not the right path, suppose '-'
// in first or last place.
if(depth == n)
{
print;
}
else
{
int i;
for(i= 0 to array.length)
{
if(array[i] is not used before)
eachPerm[depth] = array[i];
recur(depth+1, n);
}
}
}
Call this function initially recur(0, 5)