#include <BAN/Hash.h> #include <BAN/HashSet.h> #include <BAN/StringView.h> #include <BAN/Vector.h> #include <ctype.h> #include <inttypes.h> #include <stdio.h> using i8 = int8_t; using i16 = int16_t; using i32 = int32_t; using i64 = int64_t; using u8 = uint8_t; using u16 = uint16_t; using u32 = uint32_t; using u64 = uint64_t; struct Position { i64 x; i64 y; bool operator==(const Position& other) const { return x == other.x && y == other.y; } }; namespace BAN { template<> struct hash<Position> { hash_t operator()(const Position& position) const { return hash<u64>()(((u64)position.x << 32) | (u64)position.y); } }; } BAN::Vector<BAN::Vector<i64>> parse_grid(FILE* fp) { BAN::Vector<BAN::Vector<i64>> grid; char buffer[256]; while (fgets(buffer, sizeof(buffer), fp)) { BAN::StringView line(buffer); ASSERT(line.back() == '\n'); line = line.substring(0, line.size() - 1); if (line.empty()) break; MUST(grid.emplace_back(line.size())); for (size_t i = 0; i < line.size(); i++) grid.back()[i] = line[i] - '0'; } return grid; } //static constexpr i64 MIN_STEPS = 4; //static constexpr i64 MAX_STEPS = 10; template<i64 MIN_STEPS, i64 MAX_STEPS> i64 solve_general(FILE* fp) { struct Block { // heatloss[x][y]: // x: direction // y: steps left in that direction i64 heatloss[4][MAX_STEPS + 1]; i8 entered_from = -1; }; const auto grid = parse_grid(fp); // initially mark everything very large, except (0, 0) BAN::Vector<BAN::Vector<Block>> heatloss_map; MUST(heatloss_map.resize(grid.size())); for (size_t y = 0; y < grid.size(); y++) { MUST(heatloss_map[y].resize(grid[y].size())); for (size_t x = 0; x < grid[y].size(); x++) for (size_t dir = 0; dir < 4; dir++) for (size_t step = 0; step <= MAX_STEPS; step++) heatloss_map[y][x].heatloss[dir][step] = 1'000'000'000; } for (size_t dir = 0; dir < 4; dir++) for (size_t step = 0; step <= MAX_STEPS; step++) heatloss_map[0][0].heatloss[dir][step] = 0; BAN::HashSet<Position> visited; BAN::HashSet<Position> pending; MUST(pending.insert({ 0, 0 })); while (!pending.empty()) { auto position = *pending.begin(); pending.remove(position); Position offsets[4] = { { -1, 0 }, { 0, -1 }, { 1, 0 }, { 0, 1 } }; for (i8 dir = 0; dir < 4; dir++) { auto target = position; i64 path_heatloss = 0; auto is_target_in_bounds = [&](const Position& target) { if (target.y < 0 || target.y >= (i64)grid.size()) return false; if (target.x < 0 || target.x >= (i64)grid.front().size()) return false; return true; }; i64 target_distance = (heatloss_map[position.y][position.x].entered_from == dir) ? 1 : MIN_STEPS; for (i64 i = 0; i < target_distance; i++) { target.x += offsets[dir].x; target.y += offsets[dir].y; if (!is_target_in_bounds(target)) break; path_heatloss += grid[target.y][target.x]; } if (!is_target_in_bounds(target)) continue; auto& target_heatloss = heatloss_map[target.y][target.x]; bool target_updated = false; for (i8 new_dir = 0; new_dir < 4; new_dir++) { // Don't allow going backwards if (new_dir == dir + 2 || dir == new_dir + 2) continue; for (i64 step = target_distance; step <= MAX_STEPS; step++) { i64 possible_heatloss = heatloss_map[position.y][position.x].heatloss[dir][step] + path_heatloss; i64 new_dir_max_step = (new_dir == dir) ? step - target_distance : MAX_STEPS; for (i64 i = 0; i <= new_dir_max_step; i++) { if (possible_heatloss >= target_heatloss.heatloss[new_dir][i]) continue; target_heatloss.heatloss[new_dir][i] = possible_heatloss; target_heatloss.entered_from = dir; target_updated = true; } } } if (target_updated || !visited.contains(target)) MUST(pending.insert(target)); } MUST(visited.insert(position)); } i64 result = INT64_MAX; for (size_t dir = 0; dir < 4; dir++) for (size_t step = 0; step <= MAX_STEPS; step++) result = BAN::Math::min(result, heatloss_map.back().back().heatloss[dir][step]); return result; } i64 puzzle1(FILE* fp) { return solve_general<1, 3>(fp); } i64 puzzle2(FILE* fp) { return solve_general<4, 10>(fp); } int main(int argc, char** argv) { const char* file_path = "/usr/share/aoc2023/day17_input.txt"; if (argc >= 2) file_path = argv[1]; FILE* fp = fopen(file_path, "r"); if (fp == nullptr) { perror("fopen"); return 1; } printf("puzzle1: %" PRId64 "\n", puzzle1(fp)); fseek(fp, 0, SEEK_SET); printf("puzzle2: %" PRId64 "\n", puzzle2(fp)); fclose(fp); }