How to sort a std::vector of std::pairs
Sort a std::vector<std::pair<...>> in-place by the first element of the pair:
std::sort(ret.begin(), ret.end(), [](const auto& a, const auto& b) {
return a.first < b.first;
});
Sort a std::vector<std::pair<...>> in-place by the second element of the pair:
std::sort(ret.begin(), ret.end(), [](const auto& a, const auto& b) {
return a.second < b.second;
});