Are there any better methods to do permutation of string?

Question

void permute(string elems, int mid, int end)
{
    static int count;
    if (mid == end) {
        cout << ++count << \" : \" << elems << end         


        

Answer 1

Here yet another recursive function for string permutations:

void permute(string prefix, string suffix, vector &res) {
    if (suffix.size() < 1) {
        res.push_back(prefix);
        return;
    }
    for (size_t i = 0; i < suffix.size(); i++) {
        permute(prefix + suffix[i], suffix.substr(0,i) + suffix.substr(i + 1), res);
    }
}


int main(){
    string str = "123";
    vector res;
    permute("", str, res);
}

The function collects all permutations in vector res. The idea can be generalized for different type of containers using templates and iterators:

template 
void permute(typename Cont1_t prefix,
    typename Cont1_t::iterator beg, typename Cont1_t::iterator end,
    Cont2_t &result)
{
    if (beg == end) {
        result.insert(result.end(), prefix);
        return;
    }
    for (auto it = beg; it != end; ++it) {
        prefix.insert(prefix.end(), *it);
        Cont1_t tmp;
        for (auto i = beg; i != end; ++i)
            if (i != it)
                tmp.insert(tmp.end(), *i);

        permute(prefix, tmp.begin(), tmp.end(), result);
        prefix.erase(std::prev(prefix.end()));
    }
}

int main()
{
    string str = "123";
    vector rStr;
    permute>("", str.begin(), str.end(), rStr);

    vectorvint = { 1,2,3 };
    vector> rInt;
    permute, vector>>({}, vint.begin(), vint.end(), rInt);

    list ll = { 1,2,3 };
    vector> vlist;
    permute, vector>>({}, ll.begin(), ll.end(), vlist);
}

This may be an interesting programming exercise, but in production code you should use a non recusrive version of permutation , like next_permutation.