合并这两段得到什么

把 13 17 和 15 24 合成一个。

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> merge_two(const vector<int>& left, const vector<int>& right) {
    vector<int> out;
    size_t i = 0, j = 0;
    while (i < left.size() && j < right.size()) {
        if (left[i] <= right[j]) out.push_back(left[i++]);
        else out.push_back(right[j++]);
    }
    while (i < left.size()) out.push_back(left[i++]);
    while (j < right.size()) out.push_back(right[j++]);
    return out;
}

vector<int> msort(const vector<int>& a) {
    if (a.size() <= 1) return a;
    size_t m = a.size() / 2;
    vector<int> l(a.begin(), a.begin() + m), r(a.begin() + m, a.end());
    return merge_two(msort(l), msort(r));
}

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

（本题用 g++ -std=c++17 -O0 编译。）