// // Created by Matthew Gretton-Dann on 17/12/2022. // #include #include #include #include #include #include #include #include #include using Int = std::int64_t; using UInt = std::uint64_t; using namespace std::string_literals; using Shape = std::vector; auto shapes_intersect(Shape const& tower, Shape const& shape, UInt x, UInt y) -> bool { for (auto const& row : shape) { UInt cx{x}; for (auto const& c : row) { if (c != ' ' && tower[y][cx] != '.') { return true; } ++cx; } ++y; } return false; } auto tower_height(Shape const& tower) -> UInt { UInt height{tower.size() - 1}; while (tower[height].find('#') == std::string::npos) { --height; } return height; } auto main() -> int { std::string instructions; if (!std::getline(std::cin, instructions)) { std::cerr << "No input\n"; return EXIT_FAILURE; } std::string const floor{"#-------#"}; std::string const wall{"|.......|"}; Shape const horiz = {{"oooo"}}; Shape const plus = {{" o "}, {"ooo"}, {" o "}}; Shape const corner = {{"ooo"}, {" o"}, {" o"}}; Shape const vert = {{"o"}, {"o"}, {"o"}, {"o"}}; Shape const square = {{"oo"}, {"oo"}}; std::vector const shapes{horiz, plus, corner, vert, square}; // Numbers we want to store for later std::vector heights; // heights[i] gives height of tower before piece i falls. std::map wind_iter_map; // Maps place in wind string vs iteration. Used to see when we start repeating. // We have a ridiculous number of iterations to do - more than we can do on this machine so we // are going to assume that we have three phases: Setup, repeated, Teradown // We identify the repeated section by being at the same place in the instructions for Shape 0 as // we have been before. UInt previous_repeated_height{0}; Shape tower{floor}; auto wind_it{instructions.begin()}; auto shape_it{shapes.begin()}; UInt constexpr max_iter{1000000000000}; for (UInt i{0}; i < max_iter; ++i) { UInt const height{tower_height(tower)}; heights.push_back(height); if (shape_it == shapes.begin()) { // See if we've seen this wind position before for shape 0. auto [it, success] = wind_iter_map.insert({wind_it - instructions.begin(), i}); if (!success) { // We have - what is the delta in height since the last time? If it is the same delta as // the previous repeat we saw, then we can stop iterating. UInt const repeated_height(heights[it->second] - heights[i]); std::cout << "Repeated wind instruction " << it->first << ": Iters [" << it->second << ", " << i << "). Heights: [" << heights[it->second] << ", " << heights[i] << "]. Difference: " << heights[i] - heights[it->second] << ".\n"; if (repeated_height == previous_repeated_height) { break; } previous_repeated_height = repeated_height; it->second = i; } } // Where should the block appear? (2, 3 + height). UInt x{3}; UInt y{4 + height}; // Now make sure we have enough wall in the tower. while (tower.size() < y + shape_it->size() + 1) { tower.push_back(wall); } // Now do the instructions in turn: while (true) { // Wind movement UInt const trial_x{x + (*wind_it == '>' ? 1 : -1)}; if (!shapes_intersect(tower, *shape_it, trial_x, y)) { x = trial_x; } ++wind_it; if (wind_it == instructions.end()) { wind_it = instructions.begin(); } // Downward movement UInt const trial_y{y - 1}; if (!shapes_intersect(tower, *shape_it, x, trial_y)) { y = trial_y; } else { break; } } // Insert the piece. for (auto const& r : *shape_it) { UInt cx{x}; for (auto c : r) { if (c != ' ') { tower[y][cx] = '#'; } ++cx; } ++y; } // Next shape ++shape_it; if (shape_it == shapes.end()) { shape_it = shapes.begin(); } } UInt const repeat_start{wind_iter_map.find(wind_it - instructions.begin())->second}; UInt const repeat_end{heights.size() - 1}; // [0, repeat_start) is the prologue. [repeat_start, repeat_end) is repeated heights added. // [repeat_end, max_iter) is the epilogue. UInt const repeat_length{repeat_end - repeat_start}; UInt const num_repeats{(max_iter - repeat_start) / repeat_length}; UInt const num_left = max_iter - repeat_length * num_repeats; UInt const height = heights[num_left] + (heights[repeat_end] - heights[repeat_start]) * num_repeats; std::cout << "Maximum height: " << height << "\n"; return EXIT_SUCCESS; }