Find the longest contiguous sequence of integer in "a" that belongs to vector "b"

longest.cpp

#include <iostream>
#include <vector>
#include <algorithm>

using std::cout;

using Vector = std::vector<int>;

std::ostream& operator<<(std::ostream& out, const Vector& v) {
    out << "[";
    for (size_t i = 0; i < v.size(); ++i) {
        out << v[i];
        if (i != v.size() - 1) out << ", ";
    }
    out << "]";
    return out;
}

/*
 * Find the longest contiguous sequence of integer in "a" that belongs to vector "b"
*/
int main() {
    Vector a = {1, 5, 6, 1, 1, 3, 7, 8, 9};
    Vector b = {1, 3, 5};
    size_t be = 0; size_t en = 0;
    Vector r;
    for (size_t i = 0; i < a.size(); ++i) {
        if (std::find(b.begin(), b.end(), a[i]) == b.end()) {
            if (en - be > r.size()) {
                r = Vector(en - be, 0);
                std::copy(a.begin() + be, a.begin() + en, r.begin());
            }
            if (i + 1 < a.size()) be = i + 1;
        }
        en = std::max(i, be) + 1;
    }
    cout << r << '\n';
    return 0;
}