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#include <algorithm>
#include <cstdlib>
#include <fstream>
#include <iostream>
#include <iterator>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <string>
#include <string_view>
#include <vector>
using namespace std;
using graph_type = map<string, set<string>>;
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;
}
graph_type
read_file(string_view filename)
{
fstream input{ filename };
graph_type graph;
for ( string line; getline(input, line); ) {
const auto components = split(line.erase(line.find(':'), 1), ' ');
for ( size_t i = 1; i < components.size(); ++i ) {
graph[components[0]].insert(components[i]);
graph[components[i]].insert(components[0]);
}
}
return graph;
}
bool
bfs(const graph_type& graph, const string& source, const string& dest, map<string, string>& parents) // NOLINT
{
set<string> visited;
parents.clear();
queue<string> queue;
queue.emplace(source);
while ( !queue.empty() ) {
auto candidate = queue.front();
queue.pop();
if ( candidate == dest ) {
return true;
}
for ( const auto& neighbour: graph.at(candidate) ) {
if ( !visited.contains(neighbour) ) {
queue.emplace(neighbour);
parents[neighbour] = candidate;
visited.emplace(neighbour);
}
}
}
return false;
}
void
dfs(const graph_type& graph, const string& source, set<string>& visited) // NOLINT
{
visited.emplace(source);
for ( const auto& node: graph.at(source) ) {
if ( !visited.contains(node) ) {
dfs(graph, node, visited);
}
}
}
bool
bfs1(graph_type graph, const string& source, const string& dest, function<void(const string&, const string&)> visit) // NOLINT
{
set<string> visited;
queue<string> queue;
queue.emplace(source);
while ( !queue.empty() ) {
auto candidate = queue.front();
queue.pop();
if ( candidate == dest ) {
return true;
}
for ( const auto& neighbour: graph[candidate] ) {
if ( !visited.contains(neighbour) ) {
queue.emplace(neighbour);
visit(candidate, neighbour);
visited.emplace(neighbour);
}
}
}
return false;
}
void
print_graph_stats(const graph_type& graph)
{
size_t nodes = 0;
size_t edges = 0;
for ( const auto& link: graph ) {
nodes++;
edges += link.second.size();
}
cout << nodes << ", " << edges / 2 << endl;
}
void
part1(graph_type graph)
{
srand(unsigned(time(nullptr)));
vector<string> nodes(graph.size());
for ( const auto& foo: graph ) {
nodes.emplace_back(foo.first);
}
map<tuple<string, string>, int> counter;
for ( size_t idx = 0; idx != 2; ++idx ) {
for ( const auto& second: graph ) {
bfs1(graph, nodes[size_t(rand()) % nodes.size()], second.first, [&](const string& candidate, const string& neighbour) {
if ( candidate < neighbour ) {
counter[make_tuple(candidate, neighbour)]++;
}
else {
counter[make_tuple(neighbour, candidate)]++;
}
});
}
}
vector<tuple<tuple<string, string>, int>> all_links{ counter.begin(), counter.end() };
sort(all_links.begin(), all_links.end(), [](const auto& lhs, const auto& rhs) {
return get<1>(lhs) > get<1>(rhs);
});
for ( size_t i = 0; i != 3; ++i ) {
const auto [links, num] = all_links[i];
const auto [lhs, rhs] = links;
graph[lhs].erase(rhs);
graph[rhs].erase(lhs);
}
set<string> reachable;
const auto start_from_a = get<0>(get<0>(all_links[0]));
bfs1(graph, start_from_a, "--not there--", [&](const string& candidate, const string& neighbour) {
reachable.insert(candidate);
reachable.insert(neighbour);
});
set<string> reachable2;
const auto start_from_b = get<1>(get<0>(all_links[0]));
bfs1(graph, start_from_b, "--not there--", [&](const string& candidate, const string& neighbour) {
reachable2.insert(candidate);
reachable2.insert(neighbour);
});
cout << reachable.size() * reachable2.size() << endl;
}
void
print_graph(const graph_type& graph)
{
for ( const auto& node: graph ) {
cout << node.first << ": ";
copy(node.second.begin(), node.second.end(), ostream_iterator<string>(cout, ", "));
cout << endl;
}
}
graph_type
get_rgraph(const graph_type& graph)
{
graph_type rgraph;
for ( const auto& node: graph ) {
for ( const auto& link: node.second ) {
rgraph[link].insert(node.first);
}
}
return rgraph;
}
int
main()
{
auto graph = read_file("data/day25.txt");
// print_graph(graph);
part1(graph);
// print_graph(graph);
// cout << " ------------ " << endl;
// print_graph(get_rgraph(graph));
// cout << " ------------ " << endl;
// print_graph(get_rgraph(get_rgraph(graph)));
// map<string, string> parents;
// if ( bfs(graph, "jqt", "bvb", parents) ) {
// for ( const auto& [lhs, rhs]: parents ) {
// cout << lhs << ": " << rhs << endl;
// }
// }
}
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