#include #include inline constexper int TABLE[][10] = { {0, 3, 1, 7, 5, 9, 8, 6, 4, 2}, {7, 0, 9, 2, 1, 5, 4, 8, 6, 3}, {4, 2, 0, 6, 8, 7, 1, 3, 5, 9}, {1, 7, 5, 0, 9, 8, 3, 4, 2, 6}, {6, 1, 2, 3, 0, 4, 5, 9, 7, 8}, {3, 6, 7, 4, 2, 0, 9, 5, 8, 1}, {5, 8, 6, 9, 7, 2, 0, 1, 3, 4}, {8, 9, 4, 5, 3, 6, 2, 0, 1, 7}, {9, 4, 3, 8, 6, 1, 7, 2, 0, 5}, {2, 5, 8, 1, 4, 3, 6, 7, 9, 0}, }; [[nodiscard]] bool damm(std::string s) noexcept { int interim = 0; for (const auto c : s) { interim = TABLE[interim][c - '0']; } return interim == 0; } int main() { for (const auto num : { 5724, 5727, 112946, 112949 }) { if (damm(std::to_string(num))) { std::printf("%6d is valid\n", num); } else std::printf("%6d is invalid\n", num); } }