Quick Sort - C++

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

using namespace std;


void quicksort(vector<char>& vec, const int pivot_point) {
    if (vec.size() <= 1) return;

    char pivot_char = vec[pivot_point];

    vector<char> left, right;

    for (int i = 0, n = vec.size(); i < n; i++) {
        if (i == pivot_point) continue;

        if (vec[i] < pivot_char) {
            left.push_back(vec[i]);
        } else {
            right.push_back(vec[i]);
        }
    }

    if (!left.empty()) quicksort(left, rand() % left.size());
    if (!right.empty()) quicksort(right, rand() % right.size());

    vec = left;
    vec.push_back(pivot_char);
    vec.insert(vec.end(), right.begin(), right.end());
}


int main() {

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

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

    if (!vec.empty()) quicksort(vec, rand() % vec.size());

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

    cout << str << endl;
    return 0;
}