快排排完是什么样

运行下面这段程序：

#include <algorithm>
#include <iostream>
#include <map>
#include <string>
#include <utility>
#include <vector>
using namespace std;

string join(const vector<int>& v) {
    string s;
    for (size_t i = 0; i < v.size(); i++) s += (i ? "/" : "") + to_string(v[i]);
    return s;
}

vector<int> quick(const vector<int>& a) {
    if (a.size() <= 1) return a;
    int pivot = a.back();
    vector<int> less, more;
    for (size_t k = 0; k + 1 < a.size(); k++) {
        if (a[k] < pivot) less.push_back(a[k]);
        else more.push_back(a[k]);
    }
    vector<int> out = quick(less);
    out.push_back(pivot);
    vector<int> r = quick(more);
    out.insert(out.end(), r.begin(), r.end());
    return out;
}

int main() {
    cout << join(quick({17, 24, 15, 13, 23})) << endl;
}

（本题用 g++ -std=c++17 -O0 编译。）