I've never seen anyone use this in competitive programming (or anywhere really) but it might be useful:

In C++ you can use the basic_string class template instead of vector for "simple" types [1]. It works just like vector but also allows you to use a few convenient member functions and operators just like with strings, most notably operator+ and operator+=. See the following code:

#include <bits/stdc++.h>
using namespace std;

int main() {
    int n;
    basic_string<int> a;

    cin >> n;
    for (int i=0; i<n; i++) {
        int x;
        cin >> x;
        a += x;
    }

    a += a;
    a = a.substr(n/2, n);

    cout << (a + a).find({1, 2, 1}) << '\n';
}

[1] Although I'm not 100% sure, "simple" is any primitive type, std::pair of simple types, etc. Do not use this with vectors, strings, sets, maps and similar types. And for this reason please don't typedef vector as basic_string.