四种排序结果都一样吗

运行下面这段程序：

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

vector<int> bubble(vector<int> b) {
    int n = (int)b.size();
    for (int i = 0; i < n - 1; i++) {
        for (int j = 0; j < n - 1 - i; j++) {
            if (b[j] > b[j + 1]) swap(b[j], b[j + 1]);
        }
    }
    return b;
}

vector<int> insertion(vector<int> b) {
    for (int i = 1; i < (int)b.size(); i++) {
        int key = b[i];
        int j = i - 1;
        while (j >= 0 && b[j] > key) {
            b[j + 1] = b[j];
            j--;
        }
        b[j + 1] = key;
    }
    return b;
}

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() {
    vector<int> a = {17, 24, 15, 13, 23};
    vector<int> s = a;
    sort(s.begin(), s.end());
    bool same = bubble(a) == s && insertion(a) == s && msort(a) == s;
    cout << boolalpha << same << endl;
}

（本题用 g++ -std=c++17 -O0 编译。）