107 lines
2.0 KiB
C++
107 lines
2.0 KiB
C++
#include <algorithm>
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#include <cstdint>
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#include <functional>
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#include <iostream>
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#include <set>
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#include <sstream>
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#include <tuple>
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#include <doctest.h>
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#include <aocpp/Coord.hpp>
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#include <aocpp/Startup.hpp>
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using namespace aocpp;
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namespace {
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using DirFn = Coord(Coord);
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auto ToDir(char c) -> DirFn* {
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switch (c) {
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case 'L': return Left;
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case 'R': return Right;
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case 'D': return Down;
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case 'U': return Up;
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default: throw std::runtime_error{"bad input"};
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}
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}
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/// @brief Return the sign of the number
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/// @param x number
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/// @return -1, 0, or 1 matching the sign of the input
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auto Sign(std::int64_t x) -> std::int64_t
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{
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return (x>0) - (x<0);
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}
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class Logic {
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Coord knots[10] {}; // Current location of each knot in the rope
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std::set<Coord> s1{{}}, s9{{}};
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public:
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auto answer() const -> std::pair<std::size_t, std::size_t>
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{
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return {s1.size(), s9.size()};
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}
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auto move(DirFn* dirFn) -> void
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{
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knots[0] = dirFn(knots[0]);
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std::size_t k;
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for (k = 1; k < 10; ++k) {
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auto const delta {knots[k-1] - knots[k]};
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if (NormInf(delta) <= 1) {
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break;
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}
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knots[k] += {Sign(delta.x), Sign(delta.y)};
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}
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// only update the sets when a knot actually moved
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if (k > 1) {
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s1.insert(knots[1]);
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if (k > 9) {
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s9.insert(knots[9]);
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}
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}
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}
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};
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auto Solve(std::istream & in) -> std::pair<std::size_t, std::size_t>
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{
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Logic logic;
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char d;
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std::size_t n;
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while (in >> d >> n) {
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while (n--) { logic.move(ToDir(d)); }
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}
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return logic.answer();
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}
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} // namespace
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TEST_SUITE("2022-09 examples") {
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TEST_CASE("example") {
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std::istringstream in {
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"R 5\n"
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"U 8\n"
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"L 8\n"
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"D 3\n"
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"R 17\n"
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"D 10\n"
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"L 25\n"
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"U 20\n"};
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auto [p1,p2] = Solve(in);
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CHECK(p1 == 88);
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CHECK(p2 == 36);
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}
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}
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auto main(int argc, char** argv) -> int
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{
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auto [p1,p2] = Solve(*aocpp::Startup(argc, argv));
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std::cout << "Part 1: " << p1 << std::endl;
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std::cout << "Part 2: " << p2 << std::endl;
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}
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