107 lines
2.7 KiB
C++
107 lines
2.7 KiB
C++
//
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// Created by Matthew Gretton-Dann on 01/12/2022.
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//
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#include <array>
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#include <cstdlib>
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#include <iomanip>
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#include <iostream>
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#include <regex>
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#include <utility>
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using Int = std::int64_t;
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using UInt = std::uint64_t;
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constexpr char plant{'#'};
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constexpr char soil{'.'};
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unsigned encode(std::string const& s)
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{
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UInt result{0};
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for (auto c : s) {
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result <<= 1;
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result |= (c == plant) ? 1 : 0;
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}
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return result;
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}
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auto main() -> int
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{
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std::string line;
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std::regex const initial_re{"^initial state: ([#.]+)$"};
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std::regex const map_re{"^([#.]{5}) => ([#.])"};
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if (!std::getline(std::cin, line)) {
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std::cerr << "Unable to read line.\n";
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return EXIT_FAILURE;
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}
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std::smatch m;
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if (!std::regex_match(line, m, initial_re)) {
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std::cerr << "Unable to interpret: " << line << "\n";
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return EXIT_FAILURE;
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}
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std::string state{m.str(1)};
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Int state_offset{0};
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state.insert(state.begin(), 3, soil);
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state.insert(state.end(), 3, soil);
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state_offset -= 3;
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std::vector<char> transitions(32, soil);
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while (std::getline(std::cin, line)) {
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if (line.empty()) {
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continue;
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}
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std::smatch m;
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if (!std::regex_match(line, m, map_re)) {
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std::cerr << "Unable to interpret: " << line << "\n";
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return EXIT_FAILURE;
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}
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std::cout << line << "\n";
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if (m.str(2) == std::string(1, plant)) {
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transitions.at(encode(m.str(1))) = plant;
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}
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}
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for (unsigned i{0}; i < transitions.size(); ++i) {
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std::cout << ((i & 16) ? plant : soil) << ((i & 8) ? plant : soil) << ((i & 4) ? plant : soil)
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<< ((i & 2) ? plant : soil) << ((i & 1) ? plant : soil) << " => " << transitions[i]
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<< "\n";
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}
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constexpr UInt num_runs{20};
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for (UInt i{0}; i < num_runs; ++i) {
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std::cout << std::setw(2) << i << ": " << state << "\n";
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state.insert(state.begin(), 2, soil);
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state.insert(state.end(), 2, soil);
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state_offset -= 2;
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std::string next_state(2, soil);
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next_state.reserve(state.size());
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UInt encoding{encode(state.substr(0, 4))};
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for (UInt p{4}; p < state.size(); ++p) {
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encoding <<= 1;
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encoding |= state[p] == plant ? 1 : 0;
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encoding &= 31;
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next_state.push_back(transitions[encoding]);
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}
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next_state.insert(next_state.end(), 2, soil);
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assert(next_state.size() == state.size());
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state = next_state;
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}
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std::cout << std::setw(2) << 20 << ": " << state << "\n";
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Int num_plants{std::count(state.begin(), state.end(), plant)};
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Int score{0};
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Int offset{state_offset};
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for (auto c : state) {
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if (c == plant) {
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score += offset;
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}
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++offset;
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}
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std::cout << "Score: " << score << "\n";
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return EXIT_SUCCESS;
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}
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