Thread: Permutation using recursion

Hello all. I'm supposed to store a set of permutations (type list<int>) inside a set of list<int>'s. I can't figure out how to use recursion inside my permutate method. Can anyone help? I'm completely lost and this is due Monday.

Code:

#include <iostream>
#include <algorithm>
#include <list>
#include <string>
#include <cctype>
#include<set>


using namespace std;


class perm{
 
 public: 
 
 void permutate();
 void setList(int size);
 void display();


 
 
 private: 
 int max;
 list<int> numbers;
 set<list<int> > permutations;    
      
      
      
};




void perm::setList(int size)
{
   for (int i = 1; i <= size; i++)
   {
       numbers.push_back(i);
   }
  
}
   
void perm :: permutate(list<int> numbers)
{
     
     
     if (numbers.size() == 1)
     {
        permutations.insert(numbers);


     }
     else{
          
     list<int>::iterator it;
     for (it = numbers.begin(); it != numbers.end(); it++)
     {
         int c;
         c = numbers.front();
         numbers.pop_front();
         numbers.front() = c;
         
         set<list<int> > subPerms;
         subPerms = permutate(
         
         
         /*
         for (it2 = subPerms.begin(); it2 != subPerms.end(); it2++)
         {
             subPerms.insert(it2,numbers);
             numbers.pop_front();;
        
         }
         */
           
        }
        }
     
     
}
               


void perm :: display()
{
     set<list<int> >::iterator it;
     for (it = permutations.begin(); it != permutations.end(); it++)
     {
         list<int>::iterator j;
         cout << "( ";
         list<int> temp = *it;
         for (j = temp.begin(); j != temp.end(); j++) {
             cout << *j << " ";
         }
         cout << ")";
         cout << endl;
     }
}




int main()
{
    
    perm test;
    test.setList(2);
    test.permutate();
    test.display();
    
    
    
    
    
    
    system("pause");
    return 0;
}

I think this method lends itself well to recursion:
Permutation - Wikipedia, the free encyclopedia

Step one can be used as the base case for the recursion. Until the algorithm is done, you can just have your function call itself.