Quick Sort (Optimized + Insertion Sort) - C++

#include <iostream>
#include <string>
#include <vector>
#include <cstdlib>
#include <iterator>
#include <algorithm>

using namespace std;
void swap(vector<char>::iterator a, vector<char>::iterator b) {
    char tmp = *a;
    *a = *b;
    *b = tmp;
}
bool sorted(vector<char>::iterator begin, vector<char>::iterator end) {
    for (auto i = begin; i != end - 1; i++) {
        if (*(i + 1) < *i) return false;
    }

    return true;
}
void insertionsort(vector<char>::iterator begin, vector<char>::iterator end) {

    while (!sorted(begin, end)) {
        for (auto i = begin + 1; i != end; i++) {

            if (*(i - 1) > *i) {
                char hold = *i;
                auto pos = i;

                while (pos > begin && *(pos - 1) > hold) {

                    *pos = *(pos - 1);
                    pos--;
                }

                *pos = hold;
            }
        }
    }
}
void quicksort(vector<char>::iterator begin, vector<char>::iterator end) {
    /*
     * Recursion Terminating Conditions:
    */
    if (distance(begin,end) <= 1) return;
    if (distance(begin, end) <= 10) {
        insertionsort(begin, end);
        return;
    }

    vector<char>::iterator a, b;

    char pivot = *(end - 1);

    a = begin; b = end - 1;

    while(b > a) {
        if ( *(b-1) > pivot) {
            *b = *(b-1);
            b--;
        } else {
            swap(b-1, a);
            a++;
        }
    }

    *b = pivot;

    quicksort(begin, b);
    quicksort(b + 1, end);
}


int main() {

    cout << "give me a string" << endl;
    string s; getline(cin, s);

    vector<char> vec(s.begin(), s.end());

    quicksort(vec.begin(), vec.end());

    string str(vec.begin(), vec.end());

    cout << str << endl;

    return 0;
}