From 488b97ea6cda40576c4494e9e32c3b7566ee324a Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Thu, 11 Dec 2025 09:34:52 +0100
Subject: aoc 2025, day 11, part 1

---
 2025/src/day11.cpp | 85 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 85 insertions(+)
 create mode 100644 2025/src/day11.cpp

(limited to '2025')

diff --git a/2025/src/day11.cpp b/2025/src/day11.cpp
new file mode 100644
index 0000000..47440f9
--- /dev/null
+++ b/2025/src/day11.cpp
@@ -0,0 +1,85 @@
+#include <filesystem>
+#include <fstream>
+#include <functional>
+#include <iostream>
+#include <map>
+#include <set>
+#include <string>
+#include <vector>
+
+using namespace std;
+
+namespace {
+
+using Graph = map<string, set<string>>;
+
+vector<string>
+split(const string& str, const string& delims)
+{
+	vector<string> result;
+
+	size_t start = str.find_first_not_of(delims);
+	while ( start != string::npos ) {
+		size_t end = str.find_first_of(delims, start);
+
+		if ( end == string::npos ) {
+			// letzter Teil
+			result.push_back(str.substr(start));
+			break;
+		}
+
+		result.push_back(str.substr(start, end - start));
+
+		start = str.find_first_not_of(delims, end);
+	}
+
+	return result;
+}
+
+Graph
+read_file(const filesystem::path& filename)
+{
+	ifstream file{ filename };
+
+	Graph graph;
+	for ( string line; getline(file, line); ) {
+		auto parts = split(line, ": ");
+		graph[parts[0]].insert(parts.begin() + 1, parts.end());
+	}
+	return graph;
+}
+
+void
+part1(const Graph& graph)
+{
+	map<string, long> cache;
+
+	function<long(const string&)> dfs = [&](const string& src) {
+		if ( src == "out" ) {
+			return 1L;
+		}
+
+		if ( cache.contains(src) ) {
+			return cache.at(src);
+		}
+
+		long count = 0;
+
+		for ( const auto& node: graph.at(src) ) {
+			count += dfs(node);
+		}
+
+		return cache[src] = count;
+	};
+
+	cout << "Part 1: " << dfs("you") << '\n';
+}
+
+} // namespace
+
+int
+main()
+{
+	auto graph = read_file("data/day11.txt");
+	part1(graph);
+}
-- 
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