From 756f22d58bb198b8f34589c112e1003614ccdcd6 Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Sun, 2 Nov 2025 21:41:58 +0100
Subject: aoc 2017, days 1-20

---
 2017/src/day12.cpp | 115 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 115 insertions(+)
 create mode 100644 2017/src/day12.cpp

(limited to '2017/src/day12.cpp')

diff --git a/2017/src/day12.cpp b/2017/src/day12.cpp
new file mode 100644
index 0000000..66bf186
--- /dev/null
+++ b/2017/src/day12.cpp
@@ -0,0 +1,115 @@
+#include <filesystem>
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <queue>
+#include <set>
+#include <string>
+#include <vector>
+
+using namespace std;
+
+namespace {
+
+using graph_type = map<int, set<int>>;
+
+vector<int>
+split_to_int(const string& line, const string& delimiters)
+{
+	vector<int> 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(stoi(line.substr(start, end - start)));
+		}
+
+		start = end + 1;
+	}
+
+	if ( start != line.size() ) {
+		result.emplace_back(stoi(line.substr(start)));
+	}
+
+	return result;
+}
+
+graph_type
+read_lines(const filesystem::path& filename)
+{
+	ifstream   file{ filename };
+	graph_type result;
+
+	for ( string line; getline(file, line); ) {
+		auto parts = split_to_int(line, "<-> ,");
+
+		for ( size_t i = 1; i < parts.size(); ++i ) {
+			result[parts[0]].insert(parts[i]);
+			result[parts[i]].insert(parts[0]);
+		}
+	}
+
+	return result;
+}
+
+void
+bfs_mark(const graph_type& graph, int start, set<int>& seen)
+{
+	queue<int> queue;
+
+	queue.emplace(start);
+	seen.emplace(start);
+
+	while ( !queue.empty() ) {
+		int prg = queue.front();
+		queue.pop();
+
+		for ( auto link: graph.at(prg) ) {
+			if ( !seen.contains(link) ) {
+				queue.emplace(link);
+				seen.emplace(link);
+			}
+		}
+	}
+}
+
+void
+part1(const graph_type& graph)
+{
+	set<int> seen;
+
+	bfs_mark(graph, 0, seen);
+
+	cout << "Part1: " << seen.size() << '\n';
+}
+
+void
+part2(const graph_type& graph)
+{
+	set<int> seen;
+
+	int count = 0;
+
+	for ( const auto& [i, _]: graph ) {
+		if ( seen.contains(i) ) {
+			continue;
+		}
+
+		++count;
+
+		bfs_mark(graph, i, seen);
+	}
+	cout << "Part2: " << count << '\n';
+}
+
+} // namespace
+
+int
+main()
+{
+	auto data = read_lines("data/day12.txt");
+	part1(data);
+	part2(data);
+}
-- 
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