ordered_hash_map.hpp

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#ifndef ORDERED_HASH_MAP_HPP
#define ORDERED_HASH_MAP_HPP
#include <unordered_map>
#include <vector>
namespace MecaCell {
template <typename K, typename V> struct ordered_hash_map {
    // deterministic ordered hash_map
    std::unordered_map<K, size_t> um;
    std::vector<std::pair<K, V>> vec;
 
    V &operator[](const K &k) {
        if (!um.count(k)) {
            um[k] = vec.size();
            vec.push_back({k, V{}});
        }
        return vec[um[k]].second;
    }
 
    bool count(const K &k) { return um.count(k); }
    size_t size() const { return vec.size(); }
    V &at(const K &k) { return vec[um.at(k)].second; }
    void erase(const K &k) {
        if (um.count(k)) {
            const size_t id = um[k];
            if (id < vec.size() - 1) {
                vec[id] = std::move(vec.back());
                um[vec[id].first] = id;
            }
            vec.pop_back();
            um.erase(k);
        }
    }
    using const_iterator = typename decltype(vec)::const_iterator;
    using iterator = typename decltype(vec)::iterator;
    const_iterator begin() const { return vec.begin(); }
    const_iterator end() const { return vec.end(); }
    iterator begin() { return vec.begin(); }
    iterator end() { return vec.end(); }
};
}  // namespace MecaCell
#endif