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#include <cmath>
#include <filesystem>
#include <fstream>
#include <iostream>
#include <map>
#include <tuple>
#include <vector>
using namespace std;
namespace {
class UnionFind {
public:
explicit UnionFind(size_t size)
: parent_(size)
{
for ( size_t i = 0; i != size; ++i ) {
parent_[i] = i;
}
}
size_t find(size_t n)
{
if ( parent_[n] != n ) {
parent_[n] = find(parent_[n]);
}
return parent_[n];
}
void unite(size_t a, size_t b)
{
a = find(a);
b = find(b);
parent_[b] = a;
}
private:
vector<size_t> parent_;
};
using Pos = tuple<long, long, long>;
vector<Pos>
read_file(const filesystem::path& filename)
{
ifstream file{ filename };
vector<Pos> list;
long x{};
long y{};
long z{};
char ch{};
while ( file >> x >> ch >> y >> ch >> z ) {
list.emplace_back(x, y, z);
}
return list;
}
double
get_distance(const Pos& pos1, const Pos& pos2)
{
const auto [x1, y1, z1] = pos1;
const auto [x2, y2, z2] = pos2;
return hypot(x1 - x2, y1 - y2, z1 - z2);
}
void
part1(const vector<Pos>& list)
{
using Dist = tuple<double, size_t, size_t>; // (Distanz, Von, Nach)
// Distanzen paarweise erfassen...
vector<Dist> dists;
for ( size_t i = 0; i != list.size(); ++i ) {
for ( size_t j = i + 1; j != list.size(); ++j ) {
dists.emplace_back(get_distance(list[i], list[j]), i, j);
}
}
// ... und nach Distanz sortieren
ranges::sort(dists);
UnionFind unionFind(list.size());
// die kürzesten 1000 Elemente verbinden
for ( size_t i = 0; i != 1000; ++i ) {
const auto [dist, a, b] = dists[i];
unionFind.unite(a, b);
}
// die Längen der Verbindungen zählen
map<size_t, size_t> compSizes;
for ( size_t i = 0; i != list.size(); ++i ) {
compSizes[unionFind.find(i)]++;
}
// Größen finden
vector<size_t> sizes;
for ( const auto& [root, size]: compSizes ) {
sizes.emplace_back(size);
}
// Sortieren
ranges::sort(sizes, greater<>());
cout << "Part 1: " << sizes[0] * sizes[1] * sizes[2] << '\n';
}
} // namespace
int
main()
{
auto data = read_file("data/day08.txt");
part1(data);
}
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