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#include <fstream>
#include <iostream>
#include <map>
#include <set>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
vector<string>
split(const string& line, char sep = ' ')
{
vector<string> parts;
stringstream input{ line };
for ( string part; getline(input, part, sep); ) {
parts.emplace_back(part);
}
return parts;
}
template<typename Container>
string
join(const Container& container, const string& delimiter)
{
ostringstream oss;
auto it = container.begin();
if ( it != container.end() ) {
oss << *it;
++it;
}
while ( it != container.end() ) {
oss << delimiter << *it;
++it;
}
return oss.str();
}
map<string, set<string>>
read_file(string_view filename)
{
fstream input{ filename };
map<string, set<string>> data;
for ( string line; getline(input, line); ) {
const auto parts = split(line, '-');
const auto& lhs = parts[0];
const auto& rhs = parts[1];
data[lhs].insert(rhs);
data[rhs].insert(lhs);
}
return data;
}
void
part1(const map<string, set<string>>& nodes)
{
set<set<string>> connected;
for ( const auto& [node0, links]: nodes ) {
for ( const auto& node1: links ) {
for ( const auto& node2: nodes.at(node1) ) {
if ( node0 != node2 and nodes.at(node2).contains(node0) ) {
if ( node0.starts_with('t') || node1.starts_with('t') || node2.starts_with('t') ) {
connected.insert({ node0, node1, node2 });
}
}
}
}
}
cout << connected.size() << endl;
}
void
bronKerbosch(set<string> R, set<string> P, set<string> X, const map<string, set<string>>& graph, set<set<string>>& maxCliques)
{
if ( P.empty() && X.empty() ) {
// Found a maximal clique
maxCliques.insert(R);
return;
}
// Choose a pivot (heuristic: choose a vertex with maximum connections in P union X)
string pivot;
set<string> unionPX;
set_union(P.begin(), P.end(), X.begin(), X.end(), inserter(unionPX, unionPX.begin()));
if ( !unionPX.empty() ) {
pivot = *unionPX.begin(); // Choose the first vertex as pivot (simple heuristic)
}
set<string> candidates;
set_difference(P.begin(), P.end(), graph.at(pivot).begin(), graph.at(pivot).end(), inserter(candidates, candidates.begin()));
for ( const string& candidate: candidates ) {
set<string> newR = R;
newR.insert(candidate);
set<string> newP;
set<string> newX;
for ( const string& neighbor: graph.at(candidate) ) {
if ( P.find(neighbor) != P.end() ) {
newP.insert(neighbor);
}
if ( X.find(neighbor) != X.end() ) {
newX.insert(neighbor);
}
}
bronKerbosch(newR, newP, newX, graph, maxCliques);
P.erase(candidate);
X.insert(candidate);
}
}
set<string>
findLargestSet(const set<set<string>>& sets)
{
set<string> largest;
for ( const auto& sub: sets ) {
if ( sub.size() > largest.size() ) {
largest = sub;
}
}
return largest;
}
void
part2(const map<string, set<string>>& nodes)
{
set<string> R; // Initially empty
set<string> P; // All vertices are potential candidates
set<string> X; // Initially empty
for ( const auto& [vertex, _]: nodes ) {
P.insert(vertex);
}
set<set<string>> max_cliques;
bronKerbosch(R, P, X, nodes, max_cliques);
cout << join(findLargestSet(max_cliques), ",") << endl;
}
int
main()
{
auto data = read_file("data/day23.txt");
part1(data);
part2(data);
}
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