116 lines
3.0 KiB
C++
116 lines
3.0 KiB
C++
//
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// Created by Matthew Gretton-Dann on 06/12/2021.
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//
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#include <array>
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#include <cassert>
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#include <iostream>
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#include <set>
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#include <string>
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#include <utility>
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#include <openssl/evp.h>
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using MD5Digest = std::array<unsigned char, EVP_MAX_MD_SIZE>;
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enum Directions { none = 0x0, up = 0x1, down = 0x2, left = 0x4, right = 0x8 };
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auto md5_directions(std::string const& s) -> Directions
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{
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MD5Digest digest;
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EVP_MD const* md{EVP_md5()};
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unsigned int md_len{0};
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EVP_MD_CTX* md_context{EVP_MD_CTX_new()};
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assert(md_context != nullptr);
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EVP_DigestInit_ex2(md_context, md, nullptr);
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EVP_DigestUpdate(md_context, s.data(), s.length());
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EVP_DigestFinal_ex(md_context, digest.data(), &md_len);
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Directions d{Directions::none};
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if (((digest[0] & 0xf0) >> 4) > 0xa) {
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d = static_cast<Directions>(d | Directions::up);
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}
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if ((digest[0] & 0xf) > 0xa) {
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d = static_cast<Directions>(d | Directions::down);
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}
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if (((digest[1] & 0xf0) >> 4) > 0xa) {
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d = static_cast<Directions>(d | Directions::left);
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}
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if ((digest[1] & 0xf) > 0xa) {
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d = static_cast<Directions>(d | Directions::right);
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}
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return d;
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}
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struct Node
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{
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explicit Node(std::string s) : str_(std::move(s)) {}
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auto operator==(Node const& rhs) const noexcept -> bool { return str_ == rhs.str_; }
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auto operator<(Node const& rhs) const noexcept -> bool
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{
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return str_.size() < rhs.str_.size() || (str_.size() == rhs.str_.size() && str_ < rhs.str_);
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}
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[[nodiscard]] auto str() const -> std::string const& { return str_; }
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[[nodiscard]] auto x() const noexcept -> unsigned { return x_; }
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[[nodiscard]] auto y() const noexcept -> unsigned { return y_; }
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template<typename T>
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void insert_moves(T inserter) const
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{
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Directions d{md5_directions(str_)};
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if (x_ > 0 && (d & Directions::left) != Directions::none) {
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*inserter++ = Node{str_ + 'L', x_ - 1, y_};
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}
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if (y_ > 0 && (d & Directions::up) != Directions::none) {
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*inserter++ = Node{str_ + 'U', x_, y_ - 1};
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}
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if (x_ < 3 && (d & Directions::right) != Directions::none) {
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*inserter++ = Node{str_ + 'R', x_ + 1, y_};
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}
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if (y_ < 3 && (d & Directions::down) != Directions::none) {
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*inserter++ = Node{str_ + 'D', x_, y_ + 1};
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}
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}
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private:
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Node(std::string s, unsigned x, unsigned y) : str_(std::move(s)), x_(x), y_(y) {}
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std::string str_;
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unsigned x_{0};
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unsigned y_{0};
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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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if (!std::getline(std::cin, line)) {
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std::cerr << "Failed to read line\n";
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return 1;
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}
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Node initial_state{line};
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std::set<Node> visited;
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std::set<Node> to_visit;
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to_visit.insert(initial_state);
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while (!to_visit.empty()) {
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auto it{to_visit.begin()};
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Node n{*it};
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to_visit.erase(it);
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visited.insert(n);
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if (n.x() == 3 && n.y() == 3) {
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std::cout << "Movements " << n.str().substr(line.size()) << '\n';
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return 0;
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}
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else {
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n.insert_moves(std::inserter(to_visit, to_visit.end()));
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}
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}
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std::cerr << "No solution.\n";
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return 1;
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}
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