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#include <filesystem>
#include <fstream>
#include <iostream>
#include <map>
#include <string>
#include <vector>
using namespace std;
namespace {
using point_type = tuple<long, long, long>;
using particle_type = tuple<point_type, point_type, point_type>;
#if 0
ostream&
operator<<(ostream& strm, const point_type& point)
{
const auto [x, y, z] = point;
strm << '<' << x << ',' << y << ',' << z << '>';
return strm;
}
ostream&
operator<<(ostream& strm, const particle_type& particle)
{
const auto [pos, velo, accel] = particle;
strm << "p=" << pos << ", v=" << velo << ", a=" << accel;
return strm;
}
#endif
vector<long>
split(const string& line, const string& delimiters)
{
vector<long> result;
size_t start = 0;
size_t end = 0;
while ( (end = line.find_first_of(delimiters, start)) != string::npos ) {
if ( end != start ) {
result.emplace_back(stol(line.substr(start, end - start)));
}
start = end + 1;
}
if ( start != line.size() ) {
result.emplace_back(stol(line.substr(start)));
}
return result;
}
vector<particle_type>
read_file(const filesystem::path& filename)
{
ifstream file{ filename };
vector<particle_type> data;
for ( string line; getline(file, line); ) {
auto parts = split(line, "p=<>,va ");
point_type position{ parts.at(0), parts.at(1), parts.at(2) };
point_type velocity{ parts.at(3), parts.at(4), parts.at(5) };
point_type acceleration{ parts.at(6), parts.at(7), parts.at(8) };
data.emplace_back(position, velocity, acceleration);
}
return data;
}
point_type
add(const point_type& lhs, const point_type& rhs)
{
return { get<0>(lhs) + get<0>(rhs), get<1>(lhs) + get<1>(rhs), get<2>(lhs) + get<2>(rhs) };
}
void
update(particle_type& particle)
{
auto [pos, vel, acc] = particle;
vel = add(vel, acc);
pos = add(pos, vel);
particle = { pos, vel, acc };
}
long
distance(const point_type& point)
{
return abs(get<0>(point)) + abs(get<1>(point)) + abs(get<2>(point));
}
void
part1(vector<particle_type> particles)
{
size_t current_min_index = particles.size();
for ( int round = 0; round != 10000; ++round ) {
// Alle updaten
ranges::for_each(particles, update);
long step_min_dist = numeric_limits<long>::max();
size_t step_min_index = current_min_index;
// kleinste Distanz suchen
for ( size_t i = 0; i != particles.size(); ++i ) {
auto min_dist = distance(get<0>(particles.at(i)));
if ( min_dist < step_min_dist ) {
step_min_dist = min_dist;
step_min_index = i;
}
}
// Prüfen, ob stabil
if ( step_min_index != current_min_index ) {
current_min_index = step_min_index;
round = 0;
}
}
cout << "Part1: " << current_min_index << '\n';
}
void
part2(vector<particle_type> particles)
{
for ( int round = 0; round != 10000; ++round ) {
// Alle updaten
ranges::for_each(particles, update);
map<point_type, size_t> collision_counter;
for ( const auto& [pos, vel, accl]: particles ) {
collision_counter[pos]++;
}
for ( const auto& [pos, count]: collision_counter ) {
if ( count > 1 ) {
erase_if(particles, [&pos](const auto& particle) { return get<0>(particle) == pos; });
round = 0;
}
}
}
cout << "Part2: " << particles.size() << '\n';
}
} // namespace
int
main()
{
auto data = read_file("data/day20.txt");
part1(data);
part2(data);
}
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