Question

I would like to ask all my fellow programmers regarding only efficiency. I am currently solving problems that could be asked in job interviews and I’ve come across with the famous permutations of a string. The code I’ve written below might be the most common thing in programming history, however, I do not know it’s status since I haven’t checked for any solution.

Long story would the short the program I’ve coded below be a suitable solution? Or can it be made even more efficient. Asking because if I came across one day I would like to be sure that I’ve implement one of the best approaches for this problem.

#include <iostream>
using namespace std;

int fac(int num)
{
    int result=1;
    for(int i=1;i<=num;i++)
        result*=i;
    return result;
}

int main(int argc, const char * argv[])
{
    string str="abcd";
    int limit=fac(str.size());
    int mod=str.size();
    for(int i=0;i<limit;i++){
        swap(str[i%mod],str[(i+1)%mod]);
        cout<<str<<endl;
    }
    return 0;
}

Answer 1

I’ve figured out the solution by using a std::map. Don’t think it is that inefficient;

#include <iostream>
#include <map>
#include <vector>
using namespace std;

int fac(int num)
{
    int result=1;
    for(int i=1;i<=num;i++)
        result*=i;
    return result;
}
int main(int argc, const char * argv[])
{
    string str="aabb";
    int limit=fac(str.size());
    int mod=str.size();
    std::map<string,bool>T;
    vector<string>permutations;
    for(int i=0;i<limit;i++){
        if(T[str]==0){
            permutations.push_back(str);
            T[str]=1;
        }
        swap(str[i%mod],str[(i+1)%mod]);
    }
    for(int i=0;i<permutations.size();i++)
        cout<<permutations[i]<<endl;
    return 0;
}