assignment_enumerator.h

#ifndef PROBFD_PDBS_ASSIGNMENT_ENUMERATOR_H
#define PROBFD_PDBS_ASSIGNMENT_ENUMERATOR_H
 
#include <limits>
#include <ranges>
#include <span>
#include <stdexcept>
#include <vector>
 
namespace probfd::pdbs {
 
class AssignmentEnumerator {
    struct VariableInfo {
        long long int multiplier;
        int domain;
    };
 
    std::vector<VariableInfo> var_infos_;
    long long int num_assignments_;
 
public:
    AssignmentEnumerator();
 
    explicit AssignmentEnumerator(const auto& domain_sizes)
        : var_infos_(domain_sizes.size())
    {
        using namespace std::views;
        constexpr auto maxint = std::numeric_limits<long long int>::max();
 
        long long int multiplier = 1;
 
        for (auto [cur_info, domain_size] : zip(var_infos_, domain_sizes)) {
            cur_info.domain = domain_size;
            cur_info.multiplier = multiplier;
 
            if (multiplier > maxint / domain_size) {
                throw std::range_error(
                    "Construction of PDB would exceed "
                    "std::numeric_limits<long long int>::max()");
            }
 
            multiplier *= domain_size;
        }
 
        num_assignments_ = multiplier;
    }
 
    [[nodiscard]]
    unsigned int num_assignments() const;
 
    [[nodiscard]]
    unsigned int num_vars() const;
 
    [[nodiscard]]
    long long int get_multiplier(int var) const;
 
    [[nodiscard]]
    int get_domain_size(int var) const;
 
    [[nodiscard]]
    int rank_fact(int idx, int val) const;
 
    [[nodiscard]]
    std::vector<int> unrank(int assignment_index) const;
 
    [[nodiscard]]
    int value_of(int assignment_index, int idx) const;
 
    bool
    next_index(int& assignment_index, std::span<int> mutable_variables) const;
};
 
} // namespace probfd::pdbs
 
#endif // PROBFD_PDBS_ASSIGNMENT_ENUMERATOR_H