150 lines
3.1 KiB
C++
150 lines
3.1 KiB
C++
#include <cstddef>
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#include <cstdint>
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#include <iostream>
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#include <stdexcept>
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#include <sstream>
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#include <unordered_map>
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#include <unordered_set>
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#include <doctest.h>
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#include <aocpp/Grid.hpp>
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#include <aocpp/Startup.hpp>
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#include <aocpp/Coord.hpp>
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auto Part1(aocpp::Grid const &input, std::int64_t reps = 10'000) -> std::int64_t
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{
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std::unordered_set<aocpp::Coord> infected;
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// Initialize set of infected locations
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input.each([&infected](auto const pos, auto const cell)
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{
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if (cell == '#')
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{
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infected.insert(pos);
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}
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});
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// Start in the middle
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aocpp::Coord pos;
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pos.x = input.Cols() / 2;
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pos.y = input.Rows() / 2;
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// Start going "up"
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aocpp::Coord vel{.x = 0, .y = -1};
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// Count the number of iterations that cause an infection
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std::uint64_t infections = 0;
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while (reps --> 0)
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{
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auto const [it, added] = infected.insert(pos);
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if (added)
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{
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// was clean
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vel = CCW(vel); // turn "left"
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infections++;
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}
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else
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{
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// was infected
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vel = CW(vel); // turn "right"
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infected.erase(it); // clean
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}
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pos += vel; // advance
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}
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return infections;
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}
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auto Part2(aocpp::Grid const &input, std::int64_t reps = 10'000'000) -> std::int64_t
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{
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std::unordered_map<aocpp::Coord, char> cells;
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// Initialize set of infected locations
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input.each([&cells](auto const pos, auto const cell)
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{
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if (cell == '#')
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{
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cells.try_emplace(pos, '#');
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}
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});
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// Start in the middle
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aocpp::Coord pos;
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pos.x = input.Cols() / 2;
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pos.y = input.Rows() / 2;
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// Start going "up"
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aocpp::Coord vel{.x = 0, .y = -1};
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// Count the number of iterations that cause an infection
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std::uint64_t infections = 0;
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while (reps --> 0)
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{
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auto const [it, added] = cells.try_emplace(pos, 'W'); // clean becomes weakened
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if (added)
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{
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// already inserted 'W'
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vel = CCW(vel); // turn "left"
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}
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else
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{
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switch (it->second)
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{
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case 'W':
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// no turn
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it->second = '#';
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infections++;
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break;
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case '#':
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vel = CW(vel); // turn "right"
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it->second = 'F';
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break;
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case 'F':
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vel = Turn180(vel);
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cells.erase(it); // clean
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break;
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default:
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throw std::logic_error{"unexpected cell in steps"};
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}
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}
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pos += vel; // advance
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}
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return infections;
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}
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TEST_SUITE("2017-22 examples")
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{
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TEST_CASE("part 1")
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{
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std::istringstream in{
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"..#\n"
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"#..\n"
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"...\n"};
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auto const input = aocpp::Grid::Parse(in);
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CHECK(5 == Part1(input, 7));
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CHECK(41 == Part1(input, 70));
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CHECK(5587 == Part1(input, 10'000));
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}
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TEST_CASE("part 2")
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{
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std::istringstream in{
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"..#\n"
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"#..\n"
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"...\n"};
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auto const input = aocpp::Grid::Parse(in);
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CHECK(26 == Part2(input, 100));
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CHECK(2'511'944 == Part2(input, 10'000'000));
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}
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}
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auto Main(std::istream &in, std::ostream &out) -> void
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{
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auto const input = aocpp::Grid::Parse(in);
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out << "Part 1: " << Part1(input) << std::endl;
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out << "Part 2: " << Part2(input) << std::endl;
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}
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